Marsh Collection, Peabody Museum. 167 



forms of supposed Insectivora, is thus rendered possible by the 

 distinct grooves which both branches make in the under side 

 of the petrosal. In the case of all the recent forms which I 

 have examined, as well as of some of the well-known fossil 

 types, the direction of the two branches can be determined 

 with ease. 



Turning next to Primates, we find that in certain of the 

 lemurs, notably the Indrisinse and Lemuringe, the main branch 

 of the entocarotid artery enters the cranial cavity through a 

 canal at the postero-internal junction of the tympanic bulla and 

 the basioccipital, near the point of exit of the condyloid fora- 

 men, figure 101. The main artery passes forward and into the 

 cranial chamber at the side of the medulla, wholly within the 

 posterior or cerebellar fossa. In some species of these two sub- 

 families, there is a small canal entering the bulla in the posi- 

 tion corresponding to the foramen for the entocarotid in the 

 Insectivora ; this is undoubtedly the homologue of the ento- 

 carotid in that group, but it is small and inconsiderable, and 

 appears to be practically absent in all except Lemur and Pro- 

 pithecus. In these two genera, especially the latter, the tym- 

 panic branch is nearly as large as the main artery. 



In the remaining species of the living Lemuroidea, there is 

 no canal for the entocarotid in the position above described 

 for Lemur and Propithecus, but there is a large and con- 

 spicuous foramen lacerum medium, which has its usual 

 position at the antero-internal angle of the petro-tympanic, 

 figure 102. Mivart constantly spoke of this foramen as the caro- 

 tid canal, and from certain distinctive evidences of an arterial 

 vessel entering the cranial cavity in this situation, in many 

 imperfectly prepared skulls of these species which I have 

 examined, there can be apparently no doubt that the office of 

 this foramen is the transmission of the main entocarotid 

 artery. It will be thus seen that there are two distinct types 

 of entocarotid circulation in the Lemuroidea, both of which 

 are sufficiently distinct from the Insectivora to afford reliable 

 diagnostic characters. 



In the remaining Primates or Anthropoidea, including 

 Tarsius^ the entocarotid circulation presents another arrange- 

 ment. In this group, the course of the artery corresjDonds 

 more nearly with that of the Insectivora, in that its canal 

 traverses the petro-tympanic chamber. There is an important 

 difference in the two, however, for in the Anthropoidea the 

 stapedial branch of the artery is wholly wanting. The canal 

 pierces the bulla in its posterior moiety, and passing forward 

 over the cochlea, enters the cranial chamber in the middle or 

 cerebral fossa, near the posterior clinoid process, just in 

 advance of the tentorial ridge. This is evidently a superior 



