LACTEAL AND LYMPHATIC SYSTEMS. 



283 



Fig. 86. 



are now for the first time being introduced into it. That the special 



Absorbent apparatus of Vertebrated animals has for part of its functions 



to effect a change in the . materials 



absorbed, and thus to aid in fitting 



them for introduction into the blood, 



seems apparent from the facts of 



Comparative Anatomy ; which show 



that, the more distinct the blood is 



from the chyle and lymph, the more 



marked is the provision for delaying 



the latter in the absorbent system, 



and for subjecting it to preliminary 



change. 



499. The course of the Absorbent 

 vessels in Fishes is short and simple ; 

 they are not furnished with glands ; 

 and they pour their contents into 

 the blood-vessels at several different 

 parts of the body. In this class the 

 blood contains fewer red corpuscles, 

 and its coagulating power is feebler, 

 than in any other Vertebrata. And 

 in the lowest tribes, in which the 

 Vertebrated character is almost en- 

 tirely wanting, and in which the 

 blood is almost pale, no special ab- 

 sorbent system has yet been dis- 

 covered. In Reptiles, the length of 

 the Absorbent vessels is remarkably 

 increased by their doublings and 

 convolutions ; so that the system ap- 

 pears to be more highly developed, 

 than in either of the warm-blooded 

 classes. But this superiority is not 

 real ; for there is yet no trace of the 

 glands, which concentrate, as it were, 

 the assimilation power, of a long se- 

 ries of vessels. Moreover, we often 

 find the lymphatics of this class fur- 

 nished with pulsating dilatations, or 

 lymphatic hearts; which have for 

 their office to propel the lymph into 

 the venous system. In the Frog 

 there are two pairs of these ; one situ- 

 ated just beneath the skin (through 

 which its pulsations are readily seen 

 in the living animal), immediately 

 behind the hip-joint ; the other pair being more deeply seated at the 

 upper part of the chest. The former receive the lymph of the posterior 

 part of the body, and pour it into the veins proceeding from the same 



The course and termination of the Thoracic 

 Duct. 1. The arch of the aorta. 2. The thoracic 

 aorta. 3. The abdominal aorta; showing its 

 principal branches divided near their origin. 4. 

 The arteria inn'ominata, dividing into the right 

 carotid and right subclavian arteries. 5. The 

 left carotid. 6. The left subclavian. 7. The su- 

 perior cava, formed by the union of, 8, the two 

 venaj innominate; and these by the junction, 9, 

 of the internal jugular and subr-lavian vein at 

 each side. 10. The greater vena azygos. 11. The 

 termination of. the lesser in the greater vena 

 azygos. 12. The receptaculum chyli; several 

 lymphatic trunks are seen opening into it. 13. 

 The thoracic duct, dividing opposite the middle of 

 the dorsal vertebrae into two branches, which soon 

 reunite ; the course of the duct behind the arch of 

 the aorta and left subclavian artery is shown by a 

 dotted line. 14. The duct making its turn at the 

 root of the neck, and receiving several lymphatic 

 trunks previously to terminating in the posterior 

 aspect of the junction of the internal jugular and 

 subclavian vein. 15. The termination of the trunk 

 of the ductus lymphaticus dexter. 



