586 CLASS XVII. 



particular species of animals \ In some mammals the carotid artery 

 forms within the cranium around the liypopliysis cerebri a wonder- 

 net, from which the carotis cerelralis arises; it is observed in the 

 hog and the ruminants. In these animals the vertebral artery- 

 does not run to the brain, and does not penetrate the dura mater'^. 

 For other peculiarities in the course of the arteries we cannot 

 afford to delay; as, for example, that the crural arteries in the 

 cetacea, which have no hind limbs, are wanting; that the caudal 

 artery (in man the small arteria sacralis media) is very wide and 

 conspicuous in those species which have a strongly developed 

 tail, &c. As to the veins, in some there are, as in the birds, two 

 anterior or descending vence cavce, ex. gr. in the elephant, the duck- 

 mole, many rodents ; in the most, however, there is only one 

 superior cava as in man. The external jugular veins are often 

 very wide, where they convey the blood from the brain also, which 

 in man and the monkeys is performed exclusively by the internal 

 jugular veins. In the seals, the posterior cava, close to the liver, 

 has a sacciform expansion, which receives five hepatic veins, and 

 extends to the diaphragm; above the diaphragm the vein is again 

 of the common width. 



Wonder-nets occur in the vascular system of mammals at dif- 

 ferent parts of the body ; commonly they have only been investi- 

 gated on the arteries. They have been noticed on the blood-vessels 

 of the limbs in Bradypus^ Myrmecopliaga didactyla, Stenojys, Tarsius, 

 Dasypus {sexcmctus"). In the Monotremes, especially in Tachy- 

 fflossus, such vascular networks occur, but not so finely divided for 

 the limbs*. The network of the cerebral carotid we have already 



^ All these different arrangements have been observed in the human body also as 

 animal modifications of form. See J. F. Meckel Tabidce anatomico-pathologicce, 

 LipsiaB, 1820, folio, Fasc. 11. 



2 See Eapp in Meckel's ArcJdv fur Anat. u. Physiol. 1827, s. i— 13, Tab. i. 11. 



3 Carlisle was the first who observed this in the arteries of Bradypus and Stenops, 

 Philos. Transact, for 1800, Part i. p. 98. Compare on this subject amongst others 

 W, Vkolik Disquisltio de pecidiari artenarum extremitatum in nonnulUs animalihus 

 dispositione, Cum iii. Tabuhs sen. Amstelodarai, 1826, 4to; Otto in Caeds Tab. anat. 

 comp. illustr. Fasc. vi. Tab. viii. fig. 4 (veins of the lower Umbs in Bradypus tridacty- 

 lus), and Schrceder, Van der Kolk and W. Vrolik Naspxyriwjen omtrent vaatvlecJiten 

 bij onderscheidene dlervormen, in the Bijdragen tot de Dierkunde uitgegeven door het 

 GenootscJiap, Natura Artis Magistra, le Aflev. Amsterdam, 1848 (veins and arteries). 

 In Tarsias these plexuses, according to Burmeister, occur in the hind limbs only. 



4 Hyetl JDas ArterieUe Gefliss- System der Monoiremcn, Wien, 1853, 4to. 



