750 SPECIAL PHYSIOLOGY. 



fibres of the viscera of the abdomen have been proved to pass down 

 in that part of the medulla from the cerebral peduncles and optic 

 thalami. (Schiff.) 



The formation of glycogen by the liver, its conversion into sugar, 

 and the entrance of this into the blood by the veins, establish the 

 importance of this gland in the process of Sanguification. These 

 facts also suggest the possible occurrence of some similar but yet un- 

 known actions in other secreting glands, and also in such tissues as 

 muscle and nerve, as well as in the ductless glands. 



Sanguification and the Blood Grlands in Animals. 



In the Vertebra ta generally, the processes concerned in the formation of the 

 white and red corpuscles, and the fluid matrix of the blood, are similar to those 

 which occur in Man. Besides an absorbent system, the blood-glands or duct- 

 less glands, are found in all the Vertebrate Classes, but they do not all exist 

 in every Class. The spleen is almost universally present ; the suprarenal cap- 

 sules disappear earlier in the descending scale, the thyroid body and the thymus 

 still sooner. 



The spleen is present in all cases, excepting in the myxine fishes. It always 

 possesses its peculiar structure and characteristic dark red color ; it varies much 

 in shape, even in Mammalia, being, in different cases, round, oval, much elon- 

 gated, lobulated, or even multiple. The latter condition is seen in the dolphin. 

 The existence of supernumerary spleens, or splenculi, in dogs, cats, and other 

 animals, has been already mentioned. In Birds, the spleen is small, and either 

 round, oval, fusiform, or flat; in Reptiles, Amphibia, and Fishes, it is of vari- 

 able size, and differs in form according to the general shape of the body. In 

 Birds and Reptiles, this organ is usually attached to the pancreas ; in Reptiles 

 and Fishes, it is rather connected with the intestine than with the stomach, 

 as in Mammalia. The existence of the Malpighian bodies is doubtful in the 

 Amphibia, and denied in Fishes ; but the large aggregated blood-cells exist in 

 all Vertebrata. 



The suprarenal bodies are present in all Mammalia, Birds, Reptiles, in most, 

 if not all, Amphibia, and in all but the lowest Fishes. They are always of a 

 yellowish, ochreous, or golden hue. In Mammalia, they are of various forms, 

 commonly three-sided, but often elongated, cylindrical, oval, round, or even 

 crescentic. They are sometimes a little removed in position from the kidneys, 

 as in the elephant and seal. They are large in Rodentia, and small in Car- 

 nivora, especially in the seal ; their size as compared with the kidney, is, in the 

 guinea-pig, as 1 to 4; but in the seal, only as 1 to 150. In the Cetacea, they 

 are lobulated, and supernumerary suprarenal bodies are met with in many 

 animals. In Birds, these organs are small, and often lobulated. In Reptiles 

 they are usually placed on the renal veins, or vena cava inferior ; in the Ophidia, 

 the ri^ht one is the larger. In Batrachia, they are very small, broken up, or 

 often indistinct, and embedded in different parts of the kidney. In Fishes, 

 too, when present, they are usually small and multiple, and often found even 

 at the back of the kidney ; in the sturgeon and Cyclostomatous fishes, their ex- 

 istence is doubtful. 



The thyroid body is attached to the larynx in the Mammalia only. In Birds 

 and Reptiles, it is placed low down in the neck, or even in the chest, near the 

 inferior larynx. Its position seems to be regulated rather by its vascular. con- 

 nections, than by any peculiar relation to the proper larynx. In Reptiles also, 

 it is in the thoracic cavity, close above the heart. As to Fishes, it has been 

 supposed that the vascular organs known as pseudo-branchice attached to the 

 branchial apparatus, are the homologues of the thyroid body ; but the balance 

 of evidence is opposed to this view, and if the thyroid body exist at all, it is 

 only occasionally, as a small isolated mass, lying on the bulbus arteriosus. 



The thymus gland is well marked in the Mammalia, being either confined to 

 the thorax, as in the Carnivora, Insectivora, and Marsupialia, or having also 



