:](;9, PliOF. G. ELLIOT SMITH ON THE 



nnd correspondingly enlarged orbits mould the In-ain in a manner not unlike tliat 

 of Tarsliis. This avian resemblance is still further enhanced by the slender, projecting, 

 olfactory bulbs. \\n view of the fact that several well-known writers on cerebral 

 anatomy constantly refer to topographically analogous regions {e. g. the occipital " lobe "') 

 in tlie hemisplieres of birds and mammals as being homologous, I cannot too strongly 

 insist that any such jjrej)osterous suggestions are not intended in the above comparisons.] 



Gervais has already pointed out * that the brain of Tcwskis approaches nearest 

 to that of the Galagos in form. By reason of the fact that the smaller Galagina), such 

 as Microcebm, more nearly resemble Tarsias in size, it is perhaps not surprising to 

 find an even closer resemblance in the brain-form of the latter two genera. The brain 

 of Microcebus Smithi is slightly smaller than that of Tarsius f. Although the cerebral 

 hemisphere of 3Iicrocebus is 1 mm. shorter than that of Tarsias, it seems to overlap the 

 cerebellum to a slightly greater extent. The maximum depth of the hemisphere is less 

 than 1 mm. greater in Microcebus. Nevertheless the uatiform eminence (of tlie pyriform 

 lobe) apjiears to form a much more prominent boss in the latter, because it is narrower 

 and its anterior margin forms a right angle with the ventral margin of the anterior part 

 of the pyriform lobe. The smaller eyes and orbits in Microcebus lead to a much smaller 

 orbital excavation of tlie hemisphere, and consequently tlie shape of the brain is much 

 more like that of the majority of mammals. Each hemisphere of Tarsias is about 

 15 mm. broader (at its maximum diameter) than that of Microcebus. 



The oil'aciory bulb is placed almost wholly in front of the hemisphere, and is laterally 

 compressed as in the Galaginse (especially 3Hcrocehus) and the LorisiutB. In both 

 I if these respects it differs markedly from the Lemurime, Indrisinne, and Chiromys, in 

 which the bulb is flattened dorso-ventrally and overlapped by the cerebral hemisphere. 

 In Tarsius the bulb presents a triangular outline in profile, its anterior extremity 

 forming an acute angle. Its size would be regarded as very small in any other Order of 

 mammals. A comparison of the size of the bulb with that of Microcebus (which in this 

 respect may be regarded as typical of the Prosimias) shows that the olfactory bulb is less 

 than half as large as it is in the Lemurs. 



The olfactory peduncle is short and broad, as it is in all the Prosimiie and iu most 

 mammals excepting the Apes. Like that of the latter, however, and unlike that of most 

 mammals, the lumen of the peduncle and bulb is obliterated in Tarsius and other 

 Lemui"s. The short 2)eduncle of the olfactory bulb becomes continuous with a small 

 ])yriform lobe, which is placed wholly on the ventral surface of the hemisphere, forming 

 approximately tiie mesial third of the great orbital depression. The rhinal fissure 

 is almost completely obliterated, as is the case iu most Lemurs and, among small 

 njammals, the Chiroptcra. But its situation is cle.irly recognizable by the difference in 

 the appearance of the surfaces of the pyriform lobe and the neopallium, and in one 

 liemisphere a shallow furrow remains to indicate its position. There is a small tuber- 

 culum olfactorium presenting features such as are common to all mammals. 



In spite of the small size of the olfactory bulb, the hippocamjjus is relatively larger 



* .Juuin. Ac Zoologic, tome i. p. -'■>. ^ 



t III Uiis >tatement 1 ii'f'er only to t!nj ^l^el■iIla•l]^ in my J>()s>^(.•^sioIl. 



