SKULL OF A HUMAN FETUS OF 40 MM. 337 



merit in ossification of the jugular tubercle is to be noted, as this, 

 as we shall later see, is probably to be regarded as the superior 

 articular process of the occipital vertebra. 



Springing laterally and dorsally from this neural arch we find 

 the upward-shelving squama, which narrows ventrally into the 

 lamina alaris, and dorso-medially participates in the formation 

 of the tectum posterius. Its lateral portion is widened. The 

 upper border of the squama may be divided into ventral and 

 dorsal portions, the former being connected with the otic capsule, 

 and the latter with the parietal plate (figs. 3 and 5). The ven- 

 tral part is fitted closely to the caudal and dorsal surfaces of the 

 pars canalicularis of the otic capsule, the line of union being 

 crescentic in shape, with concavity looking upward, forward 

 and outward. This border extends cranio-dorsally from the 

 outer angle of the jugular foramen to the fissura capsulooccipi- 

 talis (Voit) , and its position is marked on both the inner and outer 

 aspects of the skull by crescentic grooves, formed by the approxi- 

 mation of the flattened occipital and rising otic surfaces. These 

 furrows, which may be known as the medial and lateral capsulo- 

 occipital grooves (figs. 3 and 5), are not equally well marked, that 

 on the inside of the skull being much the deeper. It contains 

 part of the transverse sinus. 



Evidence of an earlier separation between the pars canalicu- 

 laris and the squama is afforded by the microscopic appearance. 

 Between these structures there is seen, ventrally, a thin sheet of 

 perichondrium, its plane being parallel with the transverse planes 

 of the head, and when the sections are followed dorsally this 

 is found to give place to a cartilage of younger type than that 

 surrounding it, this being traceable almost as far back as the 

 capsulooccipital fissure. The younger condition of the inter- 

 vening tissue in the region of the jugular foramen as compared 

 with that farther back would seem to indicate that fusion of the 

 parts has taken place in the more dorsal part first, and has 

 gradually progressed forward, and this assumption is born out 

 by examining the illustrations of Levi. In his 14 mm. model 

 (which is the earliest stage in which the otic capsule appears) 

 the pars canalicularis and squama are almost entirely separated 



