The Cboiidrocraiiiuni of an Embryo Pig. 177 



plate. The shape of the otic region is that of a tube with walls of 

 varying thickness. Its internal surface is that of an elliptical cyl- 

 inder, while externally its surface would correspond with that of a 

 cylinder which is oval in cross-section, with the larger side ventral ; 

 the axes of the cylinder coincide and the major axes lie in the 

 sagittal plane. The crescentic spaces situated between the two cyl- 

 inders are occupied by the auditory capsules. 



Dorsally the otic ring is incomplete, no part of the chondrocranium 

 roofing over the brain except in the occipital region, as already stated. 

 The lateral walls are formed by the fenestrated and nearly vertical 

 laminw parietales and the vestibular portions of the otic capsules. 

 The basal portion of the otic region is formed by the planum basale 

 and the ventro-internal portions of the auditory capsules. It might 

 here be mentioned that in the animals below the mammals and birds 

 the otic capsules take no part in the formation of the floor of the 

 brain cavity but are located laterally and form a large portion of the 

 sides of the brain-case. As Gaupp says, the large brain of the 

 mammals has overgrown the capsules and crowded them more and 

 more ventralward. This condition reaches its highest stage in man, 

 where the ear-capsules lie almost wholly in the floor of the l^rain 

 cavity, and the foramen magnum, and even the tectum posterius, 

 have been shoved around to the ventral side. Lateral and ventral 

 to the capsules are the cartilaginous forerunners of the ear-bones, 

 together with the proximal ends of the mandibular, hyoid and 

 branchial arches. 



Dorsally the auditory capsules are bounded by the thin, slightly- 

 curved lamina parietalis (PI. Ill) which forms the greater part 

 of the lateral wall of the brain-case in this region. Whereas through- 

 out most of the head the chondrocranium is almost completely formed, 

 in the region of the lamina parietalis it still consists largely of 

 precartilaginous tissue, thus leaving several large foramina and fis- 

 sures. Later these are reduced in size or closed completely. Espe- 

 cially noteworthy is the large fissure cutting into the lamina from 

 above and behind (fis. lam. par.) It has been mentioned by several 

 authors, but no special term has been applied to it, and so I propose 

 the term fissura lamince parietalis. It is even larger in the recon- 



