250 LECTUKE X. 



corresponding witli the muscular and osseous segments of the body : 

 these 'segmental' veins consist, in the tail, of superior or neural, and 

 inferior or hcematal branches ; in the abdomen, of superior and of 

 lateral branches ; in the head, where the vertebral segments are more 

 modified, the veins manifest a less regular and appreciable corre- 

 spondence with these segments. The cephalic veins, retm-ning the 

 blood from the cranial vertebrae, their appendages and surrounding 

 soft parts, from the brain, the organs of special sense and their orbits 

 or proper cavities, from the mouth and pharynx, and, receiving also 

 the whole or part of the 'venae nutritiae' from the branchial arches, 

 unite together on each side to form a pair of 'jugular' veins, each of 

 which usually dilates into a large sinus, and again contracts and re- 

 sumes the vasiform character, as it descends to beneath the parapo- 

 physes of the atlas and axis, in order to join the corresponding trunk 

 of the vertebral veins of the body. * This great trunk, called ' vena 

 cardinalis' by Eathkef, commences at the base of the tail-fin, where 

 it receives the lymph from the pulsating sac in the Eel-tribe. The 

 ' vena cardinalis' is double, there being one for each side of the body, 

 and both right and left 'venae cardinales' extend forwards, in close 

 contact, along the hasmal canal in the tail, then through the abdomen, 

 and in both regions immediately beneath the aorta and vertebral bodies, 

 to near the ' axis,' where each trunk diverges and descends to join its 

 corresponding ' vena jugularis,' forming the short 'pre-caval' veinij: 

 {^fig. 79, e), which empties itself in the great auricular sinus between the 

 aponeurotic layers of the pericardial and abdominal septum. In the 

 Lamprey the 'vena cardinalis' is^ single along the tail, but it bifur- 

 cates on entering the abdomen into two veins, each of which is six 

 times as large as the aorta. The left cardinal vein is larger than the 

 right in the Myxinoids : but the symmetrical disposition of the ver- 

 tebral venous system is more disturbed in many osseous fishes, at the 

 expense of the right side ; the right cardinal vein, after some trans- 

 verse connecting channels with the left, finally terminating or losing 

 itself therein anteriorly : part of the right jugular vein, also, in this 



* In the Lamprey the corresponding jugular trunks lie above the aponeurotic 

 representatives of the vertebral parapophyses. 



t ' La veine cave' of Cuvier ; but it is not homologous with either the 'inferior ' 

 or ' superior venae cavae ' of Man. 



\ Ductus Cuvieri, Rathke ; quervenensfamme, Miiller. The precaval veins are 

 the homologues of the two ' superior cava ' in Reptiles and Birds, which receive 

 the so-called 'azygos' veins or reduced homologues of the 'vena cardinales' of 

 Fishes : in the higher Mammals and in Man they are concentrated into a single 

 ' superior vena cava,' receiving the ' vense cardinales ' by a common trunk, thence 

 called 'azygos' in Anthropotomy. The anatomical student is usually introduced 

 to the cardinal veins, or, to speak more strictly, their single homologue in the 

 human subject, where their normal symmetrical character becomes masked by an 

 extreme modification, and where their name is applicable only to so rare and ex- 

 ceptional a condition. 



