172 Charles Searing Mead. 



embryos, but the anterior one disappears and the other two usually 

 leave the cranial cavity through a single foramen, the foramen 

 hypoglossi (foramen spinooccipitale). Voit found that in Lepus 

 embryos two foramina hypoglossi are present on each side, and these 

 may persist even in the adult. Fischer described in an embiyo of 

 Scmnopithecus pndiwsus two hypoglossal foramina on the left side 

 and three on the right. On the other hand, his reconstruction of 

 Scmnopitliccus inaurus shows but a single foramen on each side. This 

 shows what variations may occur ^dthin the limits of a single genus 

 or even species. 



Back of the hypoglossal foramen the basal plate passes, without 

 demarcation, into the lateral walls of the occipital region. 



The union which occurs between the cochlear part of the auditory 

 capsule and the basal plate is later destroyed by the absorption of 

 the lamella of cartilage mentioned above. At this stage this lamella 

 is perforated on each side by a foramen (Pis. I and II, *, and Fig. 

 4) filled with tissue resembling precartilaginous tissue (Yorknorpel). 

 It is jorobably the homolog of the fissura basicochlearis posterior, 

 which N'oordenbos (1905) has described in embryos (14 mm.) of 

 Talpa. However this may be, this lamina fails to ossify so that in 

 the adult the foramen lacerum anterius and the foramen jugulare 

 are united by a broad slit median to the auditory bulla. 



In a Tarsius embryo of a somewhat later stage this lamina of 

 cartilage is not present and the ear-capsules are separated from the 

 planum basale for nearly their entire length by a large fissure, the 

 fissura hasicaclihans. In Talpa the large foramen piercing the 

 basis cranii median to the trabecula alicochlearis is not the foramen 

 lacerum anterius, as Fischer called it, but the fissura basicochlearis 

 anterior (ISToordenbos). It is located internally to the foramen 

 caroticum. ISTo nerves nor blood vessels pass through it, as was deter- 

 mined by examining the series of sections from which Fischer's re- 

 construction was made ; it is filled only with connective tissue. 



The foramen for the facial ner\'e, which in the reptiles pierces 

 the basis cranii anteriorly and ventrally to the ear-capsule, has here 

 migrated around to the antero-dorsal side of the cochlear portion of 

 the ear and lost completely its connection with the basal plate. This 

 will be considered in greater detail in connection with the otic region. 



