SKULL OF A HUMAN FETUS OF 40 MM. 349 



the paracondyloid foramen, and that on the right side the corre- 

 sponding area of cartilage was thin, and, further, that the Hert- 

 wig model also presented this foramen on one side. It pierces 

 the process from above downwards and forwards and is in series 

 with the costo-transverse foramina of the cervical vertebrae below. 

 If it be regarded as the costo-transverse foramen of the occipital 

 vertebra, then the bar of cartilage which closes it in front must 

 be looked upon as the costal process of this vertebra. I have 

 not been able to find that the costal process of the occipital 

 anlage has a separate center of chondrification as it has in the 

 spinal vertebrae. Though there is no vessel or nerve passing 

 through the paracondyloid foramen yet it is possible that this 

 represents an old channel of the vertebral artery, which has 

 become obsolete on account of the change of course of this vessel. 

 In this regard the foramen may be analogous to the costo- 

 transverse foramen of the 7th cervical vertebra, which no longer 

 transmits the vertebral artery. 



I regard as the representatives of the laminae the crescentic, 

 tapering, hornlike masses of cartilage which form the lateral 

 borders of the foramen magnum, and which I have spoken of as 

 the neural arches. Since the squamous portions are continuous 

 with the outer borders of these they may be considered as 

 extensions of the laminae, and the tips of the latter (dorsal 

 foraminal prominences) as the representatives of the spinous 

 processes. 



Not only on developmental, but also on histological grounds, 

 does it appear evident that the margin of the foramen magnum 

 is formed from the primitive neural arch of the occipital vertebra. 

 Upon an examination of my slides it is seen that the cartilagi- 

 nous tissue of this portion bears a strong resemblance to that 

 composing the arches of the upper cervical vertebrae, and even 

 more striking is the situation of the ossification center. It ap- 

 pears, as I have described, in the arch of the occipital vertebra, 

 just dorsal to the root of the transverse process — exactly the same 

 relative position as the ossification center in a cervical vertebral 

 arch occupies. This point is beautifully brought out in the 

 model of Hertwig, where, upon either side of the neural canal a 



