88 THE GENERAL ANATOMY OF THE LEMUROIDEA [SECT. A 



(/) The optic thalami are of unusually large dimensions in the brain 

 of the Lemur, and this development suggests high specialization of the visual 



Si'MSI'. 



(g) Judged by the appearance of the mesial sagittal section, the cerebellum 

 in the Lemurs is more developed than that of the lower mammals, and 

 approaches the form characteristic of the apes. But the lateral expansion 

 (probably in relation with the relatively small neopallium) is distinctly less 

 than in the higher Primates. 



The peripheral nervous system cannot be described here in detail. My 

 observations on Galago garnetti confirm those of Bolk 1 shewing that the 

 brachial plexus is of the " post-fixed " type 2 , as contrasted with at least 

 one frequent human type of plexus. (Of. p. 143.) 



I. Respiratory System : the Larynx. The ventricles are 

 not prolonged into the extensive sacculi so distinctive of some 

 of the higher Primates. In some Lemurs (ex. gr. Galago garnetti: 

 cf. Fig. 48) unusually large and isolated muscle-fibres are seen in 

 coronal sections of the larynx. These fibres are adjacent to the 

 M. thyro-arytenoideus (external part). 



The Trachea. This is distinguished by the fact that the 

 cartilaginous rings are complete (in Lemur), though weaker behind, 

 where the cartilage is discontinuous in other forms. 



The Lungs. The left lung has three lobes, the middle of these 

 passing into a long falciform process in front. Both the aorta and 

 the oesophagus groove this lung 3 . The right lung has (in addition 

 to the three lobes found in Man) a lobus impar which is insinuated 

 between the oesophagus behind and the post-caval vein (inferior 

 vena cava) in front. It extends thus beneath the pericardial 

 sac, being enclosed in a diverticulum (the sinus subpericar- 

 diacus) 4 . 



The pleural sacs converge behind the sternum to meet at 

 the level of the third costo-sternal joint. Thence distally they 



1 Der plexus cervico-brachialis der Primaten, Petrus Camper, Di. i. Ail. 4. 



2 Cf. Wilfrid Harris, J. A. P. July, 1904. 



3 Cf. Patten's description of the thoracic and abdominal viscera in the Trans- 

 actions of the Royal Academy of Medicine in Ireland, Vol. xvn. 1899; also in Proc. 

 Anat. Soc. 1900. Patten describes Lemur varius, while the notes above are based 

 on an examination of Lemur mongoz. 



4 Ruge, Morphologisches Jahrbuch, Band xvin. 



