290 THE BLOODVESSELS, BY C. J. EBERTH. 



primary vascular wall becomes teased out into thin trabeculse 

 and plates, varying in thickness, which are sometimes formed 

 of simple cellular threads, and sometimes of all the tissues 

 entering into its composition. 



Structures of this kind are rarely met with in the arteries. 

 The so-called carotid gland of the frog is, however, an ex- 

 ample of it. In this instance, the strong muscular wall of the 

 carotid artery forms internally a network of trabeculse, enclos- 

 ing spaces of variable size, which communicate freely with one 

 another and with the lumen of the vessel. These trabeculse 

 are simple outgrowths of the vascular wall, containing mus- 

 cle cells, which chiefly run in the oblique and longitudinal 

 direction. I cannot corroborate the statement of Leydig, that 

 these are transversely striated, but they are certainly much 

 stronger than other muscles entering into the formation of 

 vessels. 



A similar structure has been found by Retzius to occur in 

 the pulmonary arteries and aorta of the turtle. 



The structure of cavernous veins consists, in some instances, 

 of simple trabeculse of connective tissue, as in the cavernous 

 sinus, whilst in others it contains, in addition to the connective 

 tissue, bloodvessels and muscular bundles running longitudi- 

 nally, and anastomosing with one another, as in the corpora 

 cavernosa of the generative organs. The endothelium of the 

 vessels forms the innermost layer of these blood cavities. 



The cavernous capillaries repeat, on a small scale, the rela- 

 tions of the cavernous veins. In the pulmonary organs of the 

 snail the blood cavities are traversed by delicate nucleated 

 trabeculse, composed of fine homogeneous connective tissue. 

 There is here as complete an absence of a cellular investment 

 as in the great vessels of the lungs and heart * 



In the branchiae of Crustacea the framework of the blood 

 spaces is, on the contrary, composed of cells, the external ex- 

 panded extremities of which rest immediately against the cuticle 

 forming the so-called chitinogen layer, whilst the pyriform or 

 clavate bodies of the cells which conceal the nucleus are applied 



* Semper, ZeitscJirift fur wissenschaftliche Zoologie, 1856. Eberth, Blut- 

 gefdsse der Wirlellosen, " Bloodvessels of Invertebrates." 



