183] OSTEOLOGY OF LORICATI—GUTBERLET 13 



or groove, dorso-cephalad to the condyle, extending upward to the pos- 

 terior end of the temporal fossa. The lateral surface of the bone is 

 irregular in shape and possesses a broad deep groove extending from 

 slightly cephalad of the angle separating the lateral and posterior sur- 

 faces to about the middle of the prootic. At the posterior end of the 

 groove there is the foramen for the vagus nerve and slightly anterior 

 to this, another foramen for the glossopharyngeus nerve perforates the 

 bone in the same groove. On the posterior, dorsal surface, anterior to 

 the condyle, are two foramina for the passage of the occipital nerves. 

 The internal surface forms part of the posterior and part of the lateral 

 walls of the brain case and the dorsal wall of the medulla oblongata. 

 The ventro-mesial edge, overlapping the basioccipital, forms a lateral 

 recess with the groove of the basioccipital on each side of the cavum 

 sinus imparis. Dorsal to this recess, a larger cavity which lies slightly 

 dorso-cephalad to the vagus foramen, lodges the ampulla of the pos- 

 terior semicircular canal. The exoccipital unites cephalad with the 

 prootic, ventrad with the basioccipital, dorsad with the opisthotic and 

 epiotic, and mesad with its fellow from the opposite side and the supra- 

 occipital. 



Supraoccipital. — The supraoccipital (Figs. 1, 8, so) forms the 

 dorso-posterior portion of the skull, lying between the epiotics, with 

 a process between the exoccipitals, and also beneath the parietals and 

 the posterior part of the frontals, thus forming the roof of the brain 

 case as well as a part of the posterior wall. Between the epiotics it has 

 a deep groove, extending from the dorsal surface, postero-ventrad, al- 

 most to the foramen magnum, where it ends in a process between the 

 exoccipitals. The groove, the supra-temporal pocket, is formed by a 

 process on either side which overlaps the epiotics. On the dorsal sur- 

 face it has a small longitudinal crest in the median line extending 

 cephalad from the anterior end of the groove to the point where the 

 bone is overlapped by the parietals. The inner surface forms the roof 

 of the brain case as it has developed into a thin plate-like bone beneath 

 the parietals and the posterior part of the frontals. It has a smooth 

 surface with a ridge at the posterior end extending postero-ventrad 

 from the dorsal surface toward the foramen magnum. Beneath the 

 point of articulation with the parietals and frontals a small flange is 

 developed on the ventral surface near the lateral margin which extends 

 latero-cephalad, and unites with a similar flange from the sphenotic by 

 a cartilaginous ligament. In the base of the flange is a foramen for the 

 ramus lateralis accessorius vessel which passes over the supra-occipital 

 between it and the parietal. 



Basioccipital. — The basioccipital (Figs. 1, 6, 8, bo) forms the. 

 ventro-posterior end of the cranium, the posterior end of the myodome, 



