PRIMORDIAL CRANIUM OF THE CAT 289 



the dens from the ventral surface, not at its extremity, and 

 enters the hgamentum apicis dentis. It then passes over into 

 the cranium, lying at first just beneath the perichondrium of the 

 dorsal surface of the cranial floor, with the great thickness of 

 the caudal edge of the basal plate beneath it. From this point 

 the chorda dips into the cartilage of the floor as it extends for- 

 ward, lying midway between the cranial and pharyngeal sur- 

 faces in the middle third of the plate. At no point does it sink 

 nearer the pharyngeal surface nor was there observed any trace 

 of a connection with the pharyngeal wall. Proceeding toward 

 the sella turcica, the notochord gradually approaches the intra- 

 cranial surface of the basal plate, until it attains the level of the 

 dorsum sellae where it makes a rather abrupt bend so as to 

 come to lie beneath the perichondrium of the caudal surface of 

 the back of the saddle. Its terminal piece is marked by distor- 

 tion to some extent and by a few irregular turns. Although 

 shrunken in many places, and showing other evidences of de- 

 generation, the head notochord is, nevertheless, continuous 

 throughout. Within the apical Ugament it is considerably 

 expanded. 



Occipital region 



From the basal plate, the side walls of the occipital region, 

 the lateral occipital arches, continue laterally and dorsally, be- 

 coming confluent with the otic capsule, parietal plate and tectum 

 posterius (figs. 1, 2, 3, 4). They lie in a plane transverse 

 to the longitudinal axis of the posterior half of the cranium, 

 but, owing to the flexure of the long axis of the whole cranium, 

 this is at the same time, parallel with the plane of the floor of 

 the nose. 



The lateral occipital arches are connected with the pars 

 canalicularis of the otic cap.sule by synchondrosis, marked in 

 the sections by a narrow plane of young cartilage extending a 

 considerable distance from the jugular foramen toward the 

 parietal plate. Within the cranium a deep, wide groove, the 

 sulcus sigmoideus, lodging the transverse sinus, lies opposite the 

 ventral portion of the synchondrosis and leads to the jugular 



