THE VESSELS. 289 



They are, therefore, wanting in non-vascular parts, e. g. in the teeth, the 

 crystalline lens, &c. They are probably not wanting in the substance of the 

 brain, spinal cord, eye, internal ear, placenta, the membranes of the egg, and 

 the umbilical cord, although they have not been yet found in them. 



Lymphatic glands, glandules lymphaticee s. conglobata, are oval, generally 

 flattened and reddish bodies, with a smooth, even surface, and one line to an 

 inch in diam., lying generally dispersed in groups, especially in the popliteal 

 and inguinal regions, the axillary fossa in the neck, at the roots of the lungs 

 (black), in the mesentery, and in the liver (yellow), but never in the substance 

 of organs. The larger are invested by a fibrous tunic, and contain (besides 

 the numerous convolutions and ramifications of the lymphatics, besides the 

 amorphous areolar tissue, blood-vessels and nerves) small cellular spaces, 

 with granules (acini), and thus form, perhaps, actual glands, like the spleen, 

 in which the lymph obtains a particular substance, which it prepares for the 

 change into blood. Almost every lymphatic vessel passes into one of these 

 glands and out again (vasa in- and efferentia). 



A delicate capillary rete, investing the lymphatic glands and vessels very 

 abundantly, serves to nourish them. Nerve filaments have been at least 

 found in the lymphatic glands. 



527. The heart, Cor, xap&a, 



A hollow conical muscle, lies, surrounded by a serous envelope 

 (pericardium), in the centre of the thorax, between the lungs, above 

 the diaphragm, behind the sternum and before the vertebral co- 

 lumn, in rather an oblique direction from above downwards, from 

 right to left, and from behind forwards. 



It is composed of two halves, a right venous and a left arterial, 

 each of which is again separated by a septum into two commu- 

 nicating portions. The heart contains four cavities, viz. : 



the auricle (atrium) and the ventricle (ventriculus) of the 



right, and 

 the auricle and ventricle of the left side of the heart. 



The cavities are lined by tunica vasorum communis [endocar- 

 dium], the outer surfaces receive a continuation from one of the 

 layers of the pericardium. 



We have to observe of the Heart : a. the basis, that is, the 

 superior and posterior part, at which point the vessels enter and 

 from which they pass out, which lies behind the right border of 

 the Sternum, before the eighth to the sixth dorsal vertebra, and 

 is bounded by sulc. circularis. b. The apex, apex s. mitcro, ob- 

 tuse and slightly curved backwards towards the space between the 

 sixth and seventh left ribs, presents a depression, vallecula, with 

 two elevations, c. The superior, convex surface looks towards 

 the sternum, the inferior flat rests upon the diaphragm, d. The 



19 



