80 



GENERAL ANATOMY. 



smaller end being drawn out into a process which bifurcates at its extremity in a 

 T-like manner, the two limbs of the T forming the axis-cylinder of the peripheral 

 and central portions of a sensory nerve-fibre. In the sympathetic ganglia the 

 cells are multipolar, and give off a single unbranched axis-cylinder. Cells of 

 this type are found in the ciliary, spheno-palatine, submaxillary, and otic ganglia 

 attached to certain of the cranial nerves, and these may in consequence be con- 

 sidered as the cranial portion of the sympathetic system. The ganglion-cells are 

 usually enclosed in a transparent capsule with nuclei on its inner surface. The 

 nerve-fibres on entering the ganglion lay aside their perineurium, which becomes 

 continuous with the capsule. Some fibres run through the ganglion without being 

 connected with the cells. 



THE VASCULAR SYSTEM. 



The Vascular System, exclusive of its central organ, the heart, is divided into 

 four classes of vessels : the arteries, capillaries, veins, and lymphatics ; the 

 minute structure of which we will now proceed briefly to describe, referring the 



reader to the body of the work for all that 

 is necessary in the details of their ordinary 

 anatomy. 



Structure of Arteries (Fig. 57). The 

 arteries are composed of three coats : inter- 

 nal or endothelial coat (tunica intima of 

 Kblliker) ; middle muscular coat (tunica 

 media) ; and external cellular coat (tunica 

 adventitia). 



The two inner coats together are very 

 easily separated from the external, as by 

 the ordinary operation of tying a ligature 

 on an artery. If a fine string be tied for- 

 cibly upon an artery and then taken off, 

 the external coat will be found undivided, 

 but the internal coats are divided in the 

 track of the ligature and can easily be fur- 

 ther dissected from the outer coat. The 

 inner coat can be separated from the middle 

 by a little maceration, or it may be stripped 

 off in small pieces; but, on account of its 

 friability, it cannot be separated as a com- 

 plete membrane. It is a fine, transparent, 

 colorless structure which is highly elastic, 

 and is commonly corrugated into longitudi- 

 nal wrinkles. The inner coat consists of 

 1. A layer of pavement-epithelium, the cells 

 of which are polygonal, oval, or fusiform, 

 and have very distinct round or oval nuclei. 

 This endothelium, as it is now generally 

 called, is brought into view most distinctly 

 by staining with nitrate of silver. 2. A 

 subepithelial layer, consisting of delicate 

 connective tissue with branched cells lying 

 in the interspaces of the tissue. 3. An elastic or fenestrated layer, which con- 

 sists of an elastic membrane containing a network of elastic fibres, having prin- 

 cipally a longitudinal direction and in which, under the microscope, small, elon- 

 gated apertures or perforations may be seen, giving it a fenestrated appearance. 

 It was therefore called by Henle the fenestrated membrane. This membrane 

 forms the chief thickness of the inner coat, and can be separated into several 

 layers, some of which present the appearance of a network of longitudinal elastic 



FIG. 57. Transverse section through a small 

 artery and vein of the mucous membrane of the 

 epiglottis of a child. Magnified about 350 diame- 

 ters. (Klein and Noble Smith.) A. Arterv, show- 

 ing the nucleated endothelium, e, which lines it : 

 the vessel being contracted, the endothelial cells 

 appear very thick. Underneath the endothelium 

 is the wavy elastic intima. The chief part of the 

 wall of the vessel is occupied by the circular mus- 

 cle-coat m : the staff-shaped nuclei of the muscle- 

 cells are well seen. Outside this is a, part of the 

 adventitia. This is composed of bundles of con- 

 nective-tissue fibres, shown in section, with the 

 nuclei of the connective-tissue corpuscles. 

 The adventitia gradually merges into the sur- 

 rounding connective tissue, v. Vein showing 

 a thin endothelial membrane, e, raised acciden- 

 tally from the intima, which on account of its 

 delicacy is seen as a mere line on the media m. 

 This latter is composed of a few circular un- 

 striped muscle-cells, a. The adventitia, simi- 

 lar in structure to that of an artery. 



