Tag Archives: somites

39. Bones, muscles and ligaments of the pelvis. The blood vessels and nerves of the pelvis. The bone tissue. Gastrulation, early differentiation of the intraembryonic mesoderm

9 Jan

39. Bones, muscles and ligaments of the pelvis. The blood vessels and nerves of the pelvis. The bone tissue. Gastrulation, early differentiation of the intraembryonic mesoderm

Flash Cards:

Bones of Pelvis

Bones of Pelvis

Bones of Pelvis 2 - sciatic foramens

Bones of Pelvis 2 - sciatic foramens

Blood Supply of Pelvis

Blood Supply of Pelvis

Blood Supply 2

Blood Supply 2

Nerve Supply of Penis

Nerve Supply of Penis

Autonomic Nerves of Pelvis

Autonomic Nerves of Pelvis

Anatomy: Bones, muscles and ligaments of the pelvis. The blood vessels and nerves of the pelvis.

Bones & Ligaments of Pelvis

Pelvis bony girdle
2 hip bones = ox coxae, = 3 bones fused together = ilium, ischium, pubis

Pelvic Diameters of female: important for birthing processes

  • Conjugate diameters – b/w symphysis and sacral promontory = 11cm
  • Tranverse diameters – mid point of brim on each side  = 13cm
  • Oblique diameters – iliopubic eminence –> sacroiliac joint = 17.5cm
  • To set axis correctly = ASIS +pubic tubercle in vertical line


Structures to show on pelvic girdle:

  1. Pubic symphyis
  2. Iliac crest
  3. Ant sup iliac spine (attachment of inguinal lig, plus part of way to find McBurney’s pt)
  4. Greater/Lesser sciatic forament
  5. sacral promontory
  6. ischio pubic rami
  7. inf pubic rami
  8. obturator foramen
  9. acetabulum
  10. ischial spine
  11. ischial tuberosities

Pelvic Girdle

Pelvic Girdle

Divided by pelvic brim:

false pelvis above = b/w iliac wings
true pelvis below = b/w pelvic brim and outlet

Pelvic brim = pelvic inlet


  • post = sacral promontory, massa lata of sacrum
  • lat/post =arcuate line of ilum
  • lat/ant = iliopubic eminence, then pectinate line
  • ant = pubic crest, pubic symphysis

Pelvic Outlet

  • ant = inf border of pubic symphysis, arcuate ligament, inf pubic rami (making subpubic angle)
  • lat = ischial tuberosities, sacrotuberous ligaments
  • closed off by pelvic and urogenital diaphragms

M of wall of true pelvis:
Show these on speciment of dried pelvis:

  • piriformis – triangular shaped m, can identify b/c the tendon will go to gr. trochanter of femur, and you will sciatic n emerge below it
  • ob internus m – can identify b/c only n. running to obturator foramen on the inside of pelvic cavity, will wrap around and cover the obturator foramen
  • pelvic diaphragm = coccygeus + levator ani m – point to muscles that attach to coccyx
  • UG diaphragm = deep transverse perineal m, fascia *may not be able to show this*

Differences b/w Male & Female Pelvis

  • Bones thinner, smaller, lighter in female
  • Inlet heart shaped in male, oval in female – in male, sacral promontory juts into to lesser pelvis
  • Outlet larger in female > male
  • Pelvic cavity wider/shallower in female
  • subpubic angle < 90 degrees in male, and obtuse in female (>90)
    • **Good one to tell difference, if asked if pelvis is male or female
    • If the subpubic angle is the distance as you making a peace sign with your fingers = male
    • if it is the same as the angle b/w you spreading your thumb/forefinger = female
  • female sacrum shorter and wider than male
  • obturator foramen is oval or triangular in female and round in male

Joints of Pelvis

  1. Lumbosacral joint b/w L5-sacrum, held by IV disk and supported by iliolumbar ligaments, iliolumbar a from int iliac a run next to this vertically
  2. Sacroiliac joint – synovial joint of plane type b/w articular cartilage of sacrum and ilium
    • ant/post sacroiliac ligaments
    • interossesus ligaments
    • transmit weight of body from vertebral column to pelvic girdle
  3. Sacrococcygeal joint – cartiliagenous joint b/w sacrum & coccyx
    • ant, post, lat sacrococygeus lig
  4. Pubic symphysis – fibrocartiliginous joint b.w pubic bones in medial plane, anteriorally

Major Ligaments of Pelvis
— good time to mention what goes thru gr/lsr sciatic foramen

  1. Sacrospinous – from sacrum –> ischial spine
  2. Sacrotuberous – from sacrum –> ischial tuberosities
  3. ant/post sacroiliac ligaments
  4. ant/post/lat sacrococcygeal lig
  5. ant longitudial lig – runs down front of vert bodies
  6. iliolumbar lig
  7. supraspinous lig

Pelvic ligaments ant view

Pelvic ligaments ant view

Greater Sciatic notch is split into 2 sciatic foramen via sacrospinous/ sacrotuberous ligament

Greater Sciatic foramen

  • Piriformis
  • sup/inf gluteal a/v/n
  • sciatic n * show this*
  • post femoral cut n
  • int pudendal a/v
  • pudendal n

NOTE – Piriformis m further separates the greater sciatic foramen into a supra/infrapiriformic hiatus.
The only structures that go thru suprapiriformic hiatus = sup gluteal a/v/n (Supra =superior)

Rest go thru infrapiriformic hiatus, as well as n to ob internus.

CLINICAL NOTE – Because of the emergence of these structures, anasthesia can only be given in the upper R quadrant of the gluteal region, so as not to paralyze any nerves, or harm blood supply

Lesser Sciatic Foramen

  • Ob internus
  • Int pudendal a/v
  • pudendal n

Remember: the pudendal structures come out of the greater sciatic foramen–> then turn around the ischial spine –> back in thru lesser sciatic foramen –> to Alcock’s canal running in the fascia over obturator int m in ischioanal fossa

Blood Supply of Pelvis

A. Int Iliac a – @ bifurcation of common iliac a, in front of sacroiliac joint, crossed in front by ureter @ pelvic brim

Post Division
: (3) = Iliolumbar a, Lat Sacral a, Sup Gluteal a
1. Iliolumbar a – sup/lat to iliac fossa, deep to psoas major, runs straight up, next to iliolumbar ligaments
Iliac br => iliacus m, ilium
Lumbar br => psoas major, quadratus lumborum

2. Lat sacral a – passes med, in front of sacral plexus, runs immediately to sacrum
spinal br (goes thru ant sacral formina) => spinal meninges, roots of sacral n, musc/skin overlying the sacrum

3.Sup gluteal a – b/w lumbosacral trunk + 1st sacral n
-leaves pelvis thru gr sciatic foramen above piriformis m
=> m. of buttocks

Ant Division (8) = Inf gluteal a, int pudendal, umbilical a, obturator, inf vesical, med rectal, uterine
1.Inf gluteal a – b/w 1&2 or 3&4 sacral n
leaves pelvis thru gr sciatic foramen, infrapiriformic hiatus

2. Int pudendal a – leaves pelvis thru gr sciatic foramen, b/w piriformis & coccygeis  –> perineum via lesser sciatic foramen

3. Umbilical a– v. tortous a, runs along lat pelvic wall & along the side of bladder
a) Prox part –> sup vesicle a => sup bladder
a of ductus deferens => DD, seminal vesicle, lower ureter, bladder

b)Distal part –> becomes obliterated, & goes forward as medial umbilical ligament

4. Obturator a
(can also come from inf epigastric a)
pass across femoral canal –> obturator foramen
ant br => m of thigh
post br => m of thigh
-acetabular br runs to acetabular notch –> head of femur via lig. capitum femoris

5.Inf vesical a (M, vaginal a in F) => prostate, fundus of bladder, DD, seminal vesicle, lower ureter

6.Vaginal a (F from uretine a/v or int iliac a)
numerous br => ant/post wall of vagina & makes logitudinal anatomosis  in med plane to make
ant/post azygos a of vagina

7.Middle rectal a
– run med => musc layer of lower rectum & upper anal canal, prostate gland, ureter (seminal vesicles, vagina)

8.Uterine a
(Deferential a in M) – from int iliac a or w/ vaginal or middle rectal a
run med in base of broad lig –> jxn of cervix & body of uterus & runs in front of /above ureter & near lat fornix of vagina
-sup br => body + fundus of uterus
-vaginal br => cervix + vagina

B. Median sacral a

unpaired a, arising from post aspect of abdominal aorta just before bifurcation
desc in front of sacrum => post rectum, end in coccygeal body as small vascular mass in front of tip of coccyx

C Sup rectal a
– from inf mesenteric a

D. Ovarian a – one of paired visceral branches of ab aorta,
crosses prox end of ext internal a –> minor pelvis + reaches ovary thru suspensory lig of ovary

Nerve Supply to Pelvis

A. Sacral Plexus
formed by L4-5 ventral rami (lumbosacral trunk) + 1st 4 sacral ventral rami, lies on piriformis m in pelvis, below pelvis fascia

1.Sup gluteal n (L4-5) – leaves pelvis thru gr sciatic foramen, suprapiriformic hiatus
=> gluteus medius,minimus, tensor fascia lata

2.Inf gluteal n (L5-S2)
– leaves pelvis thru gr. sciatic foramen => glut max m

3.Sciatic n (L4-S3) – largest n in body
a) Tibial n = post leg
b) Common fibular = ant/lat leg
deep/sup fibular branches
composed of peroneal & tibial parts
leaves pelvis thru gr sciatic foramen, infrapiriformic hiatus
runs thigh in hollow b/w ischial tuberosity & gr. trochanter

4.N to ob internus m (L5-S2)

leaves pelvis thru gr sciatic foramen, infrapiriformic hiatus
perineum thru lesser sciatic foramen
=> ob internus, sup gemellus m

5. N to quadratus femoris (L5-S1)
leaves pelvis thru gr sciatic foramen, infrapiriformic hiatus
runs deep to gemellus m, ob internus, and ends in deep surface of quadratus femoris
=> quadratus femoris & inf gemellus m

6. Post femoral cut n (S1-S3)

leaves pelvis thru gr sciatic foramen, infrapiriformic hiatus
lie w. sciatic n and desc on back of knee
inf cluneal n, perineal br

7. Pudendal n (S2-S4)

leaves pelvis thru gr sciatic foramen below piriformis –> perineum, thru lesser sciatic foramen => bulbospongiosus, ischiocavernosus, sphincter urethrae, deep/sup transverse perineal m

8. Br to pelvis

  • n to piriformis (S1-2)
  • n to levator ani + coccygeus m (S3-4)
  • n to sphincter ani
  • pelvic splanchnic n

*** Lumbosacral trunk connect sacral/lumbar plexus (L4-S4)



Histology: The bone tissue.

Embryology: Gastrulation, early differentiation of the intraembryonic mesoderm


  • makes the 3 defined germ layer of embryo = ectoderm, mesoderm, endoderm
  • @ day 21 = called trilaminar germ disk
  • indicated by primitive streak = epiblast cells
    • primtive groove, node, and pit
    • primitive node = cephalic end of streak, elevation around the primitive pit
  • caudal to primitive streak – future anus = cloacal membrane – epiblast/hypoblast fused here
  • epiblast = ectoderm + intraembryonic mesoderm + endoderm of trilaminar disk
  • @ wk 2 – intraembryonic mesoderm begins to form organs
  • @ wk 3 – extraembryonic mesoderm begins to form placenta

Differentiation to Intraembryonic Mesoderm

1. Paraxial mesoderm – right next to midline, become somites

  • first 7 = pharyngeal arches
  • 42-44 pairs of somites from rest of them –> eventually condense to 35 pairs
  • each somite has 3 parts: sclerotome, myotome, dermatome
    • sclerotome = bones, ligaments
    • myotome = muscle
    • dermatome = skin

2. Intermediate Mesoderm – b/w paraxial and lateral mesoderm

  • forms urogenital ridge –> kidney & gonads

3. Lateral Mesoderm

  • intraembryonic coelem forms – splits lat mesoderm into 2 layers
    • somatic
    • visceral

4. Notochord – mesoderm in midline from primitive node –> prechordal plate

  • stimulates ectoderm on top –> neuroectoderm –> neural plate
  • stimulates formation of vertebral bodies & nucleus palposus

5. Cardiogenic region

  • horseshoe shaped region of mesoderm  @ cranial end of embryonic disk
  • is the future heart

2. The somatosensory and somatomotor innervation of the head and neck. The cells of the connective tissue. The development of the neurocranium.

2 Dec

2. The somatosensory and somatomotor innervation of the head and neck. The cells of the connective tissue. The development of the neurocranium.

  Flash cards:

Trigeminal n. SS of Face and some SM

Trigeminal n. SS of Face and some SM

CN VII - Facial n - SM for face

CN VII Facial N - SM for face


Cervical Plexus - SS/SM of Neck


Anatomy: The somatosensory and somatomotor innervation of the head and neck.

 This topic covers basically CN V (SS /SMof face), CN VII (SM of face), Cervical plexus (SS/SM of neck), and parts of CN IX, X, XI (flash cards of these on next topic, #2)

SS of Head & Neck

CN V = Trigeminal n

Remember = Feel the face w/ FIVE = 5th cranial nerve

  • major sensory n for face, and is motor n for muscles of mastication, and some other m.

has 3 major divisions:

Ophthalmic n: V1

  • exits skull via supraorbital fissure, w/ CN III, IV, VI, and ophthalmic v
  • innervates structures that develop from the frontonasal prominences
  • Nasociliary n
    • gives Ant ethmoid n –> gives ext nasal br = skin @ tip of nose
    • Post ethmoid n
    • Infratrochlear n = skin @ root of nose
  • Frontal n
    • Supratrochlear n – skin @ medial forehead, exit via supratrochlear foramen
    • Supraorbital n – skin @ lat forehead, exit via supraorbital foramen
  • Lacrimal n – lacrimal gland, lat upper eyelid

Maxillary n: V2

  • exits skull via foramen rotundum, into pterygopalatine fossa
  • innervates structures that develop from maxillary prominences
  • below level of eyes & above upper lip
  • Infraorbital n
    • thru infraorbital foramen, via inferior orbital fissure
    • lat side of nose, lower eyelid, upper lip
    • branches of it –> mucosa of maxillary sinus, upper inscisors, canines, and premolar teeth,  upper gingiva, hard palate
    • Ant, Mid, Post, Sup alveolar n forms maxillary dental plexus
  • Zygomaticotemporal n
    • from foramen of same name
    • skin over ant temporal region
  • Zygomaticofacial n
    • foramen of same name
    • skin over zygomatic region
    • carries post-ggl fibers from pterygopalatine ggl, via Gr palatine, Lsr palatine, & Nasopalatine n, to Lacrimal n

Mandibular n: V3

  • exits skull via foramen ovale
  • aff/eff branch of jaw jerk reflex
  • innervates structures that develop from mandibular prominences
  • level of lower lip and below
  • Inf alveolar n
    • goes thru mandibular canal and emerges from mental foramen as mental n
    • supply lower teeth, chin, lower lip
  • Auriculotemporal n
    • crosses root of zygomatic process –> temporal region deep to sup temporal a, encircles around middle meningeal a
    • supply ext acoustic meatus, tympanic mem, auricle
  • Buccal n
    • only sensory br of motor div. of V3
    • deep to ramus of mandible –> runs ant and thru buccinator
    • supplies mucus membrane lining cheek, post part of buccal surface of gum
  • Lingual n
    • SS to ant 2/3 of tongue
  • SM = MOTOR branches –> m. of mastication, ant digastric, mylohyoid m, tensor veli palatini, tensor tympani

CN VII Facial n = SM of face

  • has motor and sensory roots,
  • SM = all muscles of facial expression, including platysma, auricularis m, post digastric m, stylohyoid m, stapedius m
  • supplies structures developing from 2nd pharyngeal arch
  • VS = taste to ant 2/3 of tongue – via Chorda Tympani (discussed in next topic)
  • SS = w/ auricular branches from IX, X –> fibers to external ear, tympanic mem
  • Pathway: IAM –> petrous part of temporal bone (through auditory canal) —> exit skull via stylomastoid foramen
  • Once exits, gives off Post auricular n = m of auricle, occipitalis m, EAM, w/ branches from CN IX, X
  • runs ant and through parotid gland, where it gives its 5 terminal branches
  • NOTE DOES NOT INNERVATE PAROTID GLAND, merely runs through it

Terminal branches:

  • Temporal – m of forehead, orbicularis oculi
  • Zygomatic – m. over zygomatic bone, orbital and infraorbital m
  • Buccal – Buccinator m, m of upper lip
  • Mandibular (marginal)- m. of chin, lower lip
  • Cervical – platysma, *w/transverse cervical n. of Cervical plexus

Cervical Plexus:

  • from primary ventral rami of C1-C4, emerge next to ant scalene m
  • ant branches = SM, post branches = SS to anterolat neck, sup part thorax

SS of Neck = cutaneous branches of Cervical plexus – see note card at start of this post

  1. Lesser Occipital (C2,3) –  scalp behind ear
  2. Greater Auricular (C2,3) – scalp around auricle, and parotid region
  3. Transverse Cervical (C2,3) – skin of ant cervical triangle
  4. Supraclavicular  n (C3,4) – ant, mid, post br to skin of clavicle and shoulder
  5. NOTE = NOT A BRANCH OF CERVICAL PLEXUS, but does SS of head/neck – Greater Occipital n (dorsal rami of Cervical spinal n) – post part of scalp

SM of Neck =  2 major motor branches of cervical plexus, + many side motor branches

  • Branches not from Cervical Plexus
    • ventral rami of cervical nodes – SM to rohomoids, serratus ant, prevertebral m
  • Ansa Cervicalis
    • union of sup root (C1-2) + inf root (C2-3)
    • superior and w/in carotid sheath in ant cervical triangle
    • supplies infrahyoid m, except thyrohyoid (C1 via CNXII)
  • Phrenic n – not technically part of neck, but part of plexus
    • arises C4, but rec branches from C3-4
    • has SM, SS, SNS n fibers
    • SM to lat diaphragm, SS to central tendon
    • desc on ant surface of ant scalene m under SCM
    • passes b/w subclavian a/v  –> thorax, joins pericardiophrenic br of int thoracic a
    • SS = mediastinal pleura
  • SM br off plexus= longus capitis, longus cervicis, Levator scapulae, scalene m
  • Acc phrenic n –  occasional br of plexus, from C5 and joins phrenic n below 1st rib

 SS/SM innervation from other CN:

  • CN IX =
    •  SS to post 1/3 of tongue, palatine tonsil & soft palate, tympanic cavity, mastoid antrum, auditory tubes, ext ear
    • SM to stylopharyngeus m,
  • CN IX, X, XI = give fibers to the common pharyngeal plexus
    • SM = m. of pharynx, larynx, palate except tensor veli palatini (V3)
  • CN XI
    • SM = SCM, trapezius
    • as mentioned above, is part of pharyngeal plexus
    • spinal roots from ant horn of upper cervical segments, emerge from dorsal/ventral roots of spinal n – combine to form 1 trunk –> enter skull via foramen magnum
    • also exits via jugular foramen
  • CN X
    • Superior Laryngeal n
      • Int laryngeal n – SS to larynx above vocal fold, lower pharynx, epiglottis
      • Ext laryngeal n – SM to cricothyroid, inf pharyngeal constrictor m.
    • Recurrent laryngeal n
      • hooks around subclavian a on R, and arch of aorta on L (lat to lig arteriosum)
      • asc in groove b/w trachea & esophagus
      • SS = larynx below vocal cord
    • SS from all mucus membranes = lower pharynx, larynx, and down to all thoracic/abdominal organs



    Histology:The cells of the connective tissue.

     There are two types of Connective Tissue cells:

    1. Resident cells – have their own motility within tissue. ex/ histocyte, mast cell, adipocytes, smooth m cells, plasma cells, fibroblasts
    2. Transient cells – move in and out of tissue, ex/ WBC – lymphocytes, granulocytes, monocytes

    Cells of CT:

    • fibroblasts –
      • elongated cell w/ cytoplasmic extensions
      •  ovoid nucleus, sparse chromatin, 1 or 2 nuclei
      • = synthesize  collagen, reticular, elastic fibers, and carbs of ECM
    • fibrocyte –
      • more mature, smaller splindle shaped cells 
      •  no cytoplasmic extentions, smaller nucleus than fibroblast
      • = less active, but same function as fibrocyte
    • plasma cell –
      • smaller, accentric nucleus, with condensed chromatin,
      • oval shape, cytoplasm mostly clear
      •  = secrete immunoglobulins & develop from B cells
    • adipose cell –
      • narrow rim of cytoplasm, flat accentric nucleus
      • large and mostly empty cytoplasm
      • =  store fat
    • lymphocyte – 
      • spherical shaped ells, dense chromatin in central nucleus,
      • no nucleoli
      • = mediate immune response, produce antibodies, defend body against infections, secrete proteins
    • macrophages –
      • round, irregular cell outlines, small nucleus rich in chromatin,
      • cytoplasm filled w/ injested particles,
      • have feet like extensions called “pseudopodia”,
      • eosinophillic due to increased # of lysozymes
      • = phagocytes that injet bacteria, dead cells, cell debris, are Antigen presenting cells = APCs, also aid in immune response
      • * Look for fuzzy reddish ovoid structure with many spots in cytoplasm – can be found near a/v, but unlikely you would be asked to identify one
    • eosinophil –
      • large WBC w/ bilobed nucleus *like headphones*,
      • large eosinophillic granules in cytoplasm – red color
      • = inc in # after parasitic infections or allergic reactions, phagocytose Antigen-antibody complexes after infection
    • neutrophil –
      •  large WNC with many lobed nucleus, no granules in cytoplams,
      • cytoplasm more or less unstained
      • = engulf and destroy bacteria @ infection sites
    • mast cell –
      • ovoid or circular, small central nucleus,
      • basophillic cytoplasm filled w/ fine closely packed, dense staining granules of histamine and heparin
      • = synthesize and release heparin and histamine.
        • Heparin = weak anticoagulant,
        • Histamine = used in inflammatory response, dilates a/v, increase a/v permiability to fluid, induces signs of allergic reaction
    • monocytes –
      • largest  WBC, bean shaped nucleus
      • become macrophages
      • part of MPC = Mononuclear Phagocytotic System
      • = clean up tissue, antigen presentation = APCs

    Embryology:The development of the neurocranium.

    • skeletal system develops from paraaxial, lateral plate mesoderm, & neural crest
    • Paraxial mesoderm forms somites,t hat split into somitomeres, dermatomes, & myotomes
    • @ 4th week -sclerotomes –> become mesenchyme (embryonic CT)
    • Mesenchyme can form many things, like osteoblasts = bone forming cells
    • Neural crest cells in head region can also become mesenschyme
    • 2 types of bone formation:
      • (Intra)membranous ossification –  mesenchyme of dermis is converted right to bone
      • Endochondral ossification – mesenchyme –> hyaline cartilage –> ossified by osteoblasts

    Neurocranium = forms protective case around brain
    Two parts:
    1. Membranous part = flat bones, like Parietal, Frontal, Squamous part of temporal and occipital
    2. Cartilaginous part = bones @ base of skull, like ethmoid, sphenoid, petrous part of temporal and occipital

    Membranous Neurocranium

    • from para-axial mesoderm and neural crest cells
    • undergo membranous ossification
      • is the aggregation of mesenchyme cells in the area where bone is to be formed.
      • The tissue in this area becomes more vascularized, 
      •  mesenchyme cells begin to differentiate into osteoblasts,
      • osteoblasts secrete the collagen and ground substance (proteoglycans) of bone matrix (collectively called osteoid).
      • The osteoblasts maintain contact with one another via cell processes.
      •  The osteoid becomes calcified with time, and the processes of the cells (called osteocytes when they are surrounded with matrix) become enclosed in canaliculi.
      • Some of the mesenchymal cells surrounding the developing bone spicules proliferate and differentiate into osteoprogenitor cells.
      •  Osteoprogenitor cells in contact with the bone spicule become osteoblasts, and secrete matrix, resulting in appositional growth of the spicule.
      • Intramembranous ossification begins at about the eighth week in the human embryo.
    • bone spicules  grow from primary ossification centers –>periphery
    • bones grow by adding new membranous layers on the outside, and at the same time, resorption of inner layers by osteoclasts inside

    On Newborn skull,  the flat bones of skull are not united. In fact, you don’t want them to be, as the movement of these bones against each other allow the head to be shaped in certain ways to make birth easier.

    At this point, the flat bones are separated by CT sutures:

    • sagittal suture – from neural crest cells, b/w two  parietal bones
    • coronal suture – from paraaxial mesoderm, b/w frontal and parietal bones

    Where more than 2 bones meet = fontanelle

    • ant fontanelle – where 2 frontal/2 parietal meet, will close w/in 2 years (like mastoid fontanelle) to become bregma
    • post fontanelle – where 2 pariteal/occipital meet, will close w/in 6 months (like sphenoid fontanelle) to become lambda
    • some sutures remain open until adulthood

    Chondrocranium & Cartilaginous Neurocranium

    • formed by many cartilages
    • prechordal chondrocranium
      • lie in front of rostral (front/ant) end of notochord (future spinal cord) — hence, prechordal
      • post border = sella turcica
      • neural crest origin
    • chordal chondrocranium
      • lie behind  sella turcica
      • develop from occipital somites = para-axial mesoderm origin
      • is the area that will surround the future spinal code — hence, chordal.