MAMMALS. 597 



The cerebral nerves correspond to those of man. The first 

 pair, however, forms in some degree an exception, for though not 

 indeed absent in all true Cetacea, it is wanting in the dolphins 1 . In 

 most mammals (the apes alone with the seals and those cetaceans 

 which possess olfactory nerves make an exception here) the olfac- 

 tory nerves are thick and have a cavity internally, which is a 

 prolongation of the lateral ventricles, just as the nerves also 

 (processm mamillares) exhibit themselves as prolongations of the 

 cerebrum. The fifth pair of nerves, forming principally the nerves 

 of sensation for the head, and sending branches to all the organs of 

 sense, is in many mammals of peculiar strength and thickness when 

 compared with that pair in man 2 . 



The nervous system of organic life, the great sympathetic, is 

 formed, as far as investigations indicate, essentially as in man. 

 This system is situated in great part in the cavities of the thorax 

 and abdomen, and follows the course of the vessels. The largest 

 plexus (plexus cceliacus s. Solaris) lies behind the stomach, princi- 

 pally round the cceliac artery. The great sympathetic is connected 

 by many branches and in various situations with the nervous sys- 

 tem of animal life, in part supplying and in part receiving the 

 nervous filaments 3 . The spinal nerves are connected both by 

 their anterior (inferior or motor) roots, and by their posterior 



on the convolutions of the cerebrum) may be consulted with advantage on the brain of 

 mammals. The mammals have in general behind the pons on each side a small 

 transverse band of fibres at the origin of the seventh and eighth pair ; this part, which 

 TREVIRANUS names trapezium, is absent in man (but not in the apes). The lateral 

 ventricals of the brain have, with the exception of the apes and some others, no pos- 

 terior horn, and thus also no pes Hippocampi minor. TBEVIE. Verm. Schr. in. s. 4, 5. 



1 STANNIUS Ueber den Bau des DelpJiin-Gehirns; Abhandlungen Tierausgegeb. von 

 dem natwrwissenschaftlichen Verein in Hamburg, I. 1846 ; see especially s. 4, and Tab. 

 H. base of the brain. In Hyperoodon, on the other hand, ESCHRICHT has described 

 and figured the first pair of nerves. Kongel. DansTce Videnskabernes Selskabs Naturvi- 

 densk. Afhandlinger, xi. 1845, P- 3^o, Tab. vin. In Balcena OWEN describes these 

 nerves as not dissimilar to those of man ; HUNTER Animal (Economy, pp. 367, 368. 



2 Compare W.RAPpDieVerrichtungendesfunftenHirnnerven-Paares, Leipzig, 1832, 

 4to. For the comparative anatomy of the cerebral nerves in mammals there are several 

 important contributions by and under the guidance of Prof. BONSDORFF of Helsingfors, 

 and amongst them, in the dog, the first six pairs of nerves by V. HABTMANN (1846), 

 and the last six pairs by PIPPING (1847), described in two (Swedish) dissertations 

 defended at the University. 



3 See amongst others F. ARNOLD Der KopftJieil des vegetativen Nerven-Systems beim 

 Menschen, Heidelberg u. Leipzig, 1831, 4to. 



II 



