166 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



the parachordal cartilages, two cartilaginous bars which partly 

 surround the cranial part of the notochord (Figs. 133 and 121). 

 The parachordal cartilages represent in the skull the cartilaginous 

 sheath of the notochord out of which, in the spinal column, the 

 bodies of the vertebrae are developed. Each cartilage throws 

 out a wing (Fig. 134); these meet over the hind brain and 

 form the exoccipitals and cartilaginous part of the supra-occipital, 



font, at 

 asterion 



parietal 

 —lambda 



suora-occip. 

 (memb.) 



fontanelle 

 petro-mast. 

 supra-occ. (cartil) 

 oceip.font 

 atlas 

 axis 



Fig. 132. — The Occipital Region in a Foetus of 5 months. 



and thus enclose the foramen magnum. In Fig. 132 the con- 

 dition of the occipital region is shown in a 5 th -month foetus. 

 The supra-occipital parts of the parachordal cartilages have fused. 

 A suture between the membranous and cartilaginous parts is 

 clearly visible — especially near the fontanelle at the asterion. 

 The membranous and cartilaginous parts of the supra-occipital 

 become completely fused soon after birth. It will be observed 

 that the process of fusion between the lateral parts of the cartila- 

 ginous supra-occipital is not complete at the 5th month (Fig. 132). 

 The occipital fontanelle (Sutton) projects upwards between them 

 from the foramen magnum (Fig. 132). This fontanelle is filled 

 by a continuation of the posterior atlanto-occipital ligament ; and 

 becomes closed soon after birth. It is the most common site of a 

 cerebral meningocele — a saccular protrusion of the membranes of 

 the brain which contains cerebro-spinal fluid, and possibly also 

 a part of the brain. 



