PRIMORDIAL CRANIUM OF THE CAT 291 



and glossopharyngeus nerves pass straight through the foramen. 

 Although the paracondyloid process forms a deep wall for the 

 foramen posteriorly, there is no inclination forward of this pro- 

 cess nor a lamina alaris with attendant horizontal course of the 

 nerves. On the extracranial surface, the foramen is divided into 

 cephalic and caudal parts by an angular process of the cochlear 

 wall (figs. 12, 19). The compartment posterior to the process 

 is occupied by the jugular vein and the group of nerves; the 

 anterior compartment, filled with connective tissue, lies within 

 the fenestra perilymphaticum and forms a communication be- 

 tween the cavum cochleae and fossa occipito-canalicularis ; it is 

 the beginning of the aquaeductus cochleae. 



The hypoglossal canal (figs. 1, 2, 12) transmits the three pre- 

 viously united ventral roots of the hypoglossal nerve. It runs 

 in a ventro-lateral direction, beginning caudad and medialward 

 of the jugular foramen and terminating on the external surface 

 at the level of the medial edge of the paracondyloid process. 



The broad, square paracondyloid process (figs. 2, 3, 12, 19) 

 projects widely from the ventral part of the pars lateralis of the 

 occipital region, with ventral and lateral free edges, cephalic 

 and caudal surfaces. The narrow cephalic surface enters into 

 the wall of the jugular foramen; the ventral broad free edge is 

 continuous medially with that part of the extracranial surface 

 lying between the jugular foramen and the hypoglossal canal. 



The foramen magnum (figs. 1, 2) is hexagonal with 

 rounded angles, the sides consisting of the free caudal margins 

 of the basal plate and lateral occipital arches and, dorsally, 

 the edge of the spino-occipital membrane. The foramen is 

 divisible into a large ventral part included between the condy- 

 lar portions of the occipital arches, and a smaller dorsal region 

 extending thence to the spino-occipital membrane. The lateral 

 boundaries of these two divisions come together in a notch of the 

 lateral occipital wall just dorsad of each condyle (figs. 1, 2, 

 3, 4). A number of small veins in the connective tissue of 

 these notches, were connected with the sinus transversus. The 

 plane of the whole foramen magnum is nearly transverse to the 

 longitudinal axis of the posterior half of the cranium; however, 



