DIAPHRAGMATIC NERVE. 859 



the preceding, and is distributed to the sphincter ani muscle and the surround- 

 ing integuments. Before quitting the pelvis, it gives a ramuscule to the 

 levator ani. 



The five inferior sacral branches emit, near their origin, a more or lesa 

 slender filament that proceeds to the pelvic or hypograstic plexus. The anasto- 

 mosing divisions, through which they communicate with the sympathetic chain, 

 are generally thick, short, and multiple. 



Aeticle v.— Coccygeal Neeves (6 to 7 Paies). 



In the coccygeal region are found two pairs of nerves — one placed beneath 

 the compressor muscle of the tail, the other below the curvator muscle. These 

 two nerves extend to the extremity of the tail, throwing off on their track some 

 muscular and cutaneous filaments. They are formed by the superior and inferior 

 branches of the coccygeal nerves, which gradually amalgamate to form the two 

 nerves. 



These coccygeal branches are six or seven in number, and very distinct ; they 

 diminish in volume from the first to the last. The first only gives a slender 

 filament for the formation of each coccygeal trunk ; it is chiefly expended in the 

 integuments and muscles at the base of the tail. 



Aeticle VI. — Composite Neeves foemed by the Infeeioe Beanches op 

 THE Spinal Neeves. 



We already know that these nerves represent three groups : 1. The dia- 

 vhragmatic nerve. 2. The brachial plexus. 3. The lumbosacral plexus. They 

 will be studied in this order. 



Diaphragmatic (or Phrenic) Nerve. 



The diaphragmatic nerve (the internal respiratory nerve of Bell) is formed by 

 two principal branches, and a small accessory ramuscule, the presence of which 

 is not constant. The latter comes from the fifth cervical pair ; the two others 

 proceed, one from the next pair, the other from the brachial plexus. The branch 

 from the sixth pair pierces the inferior scalenus muscle from within to without, 

 gives off a filament to the brachial plexus, and descends obliquely backAvards to 

 the surface of the muscle it passes through, to unite — at the entrance to the 

 chest — with the branch of that plexus. This latter branch, generally shorter and 

 thicker, comes exclusively from the seventh cervical pair. 



The trunk of the diaphragmatic nerve, formed in this manner, passes into the 

 thorax after receiving the branch of the fifth pair — when it exists — passes within 

 the axillary artery, along with the pneumogastric nerve, and often at this point — 

 if not always — obtains a filament from the sympathetic. It then gains the side 

 of the base of the heart, passing beneath the pleura, and finally attains the tendi- 

 nous centre, after a course of at least eight inches between the two layers of the 

 posterior mediastinum — the left nerve being in the mediastinum proper,^ while that 

 of the right side lies in the special serous partition for the posterior vena cava. 



' Lesbre has found, in an Ass, an anomaly in the course of the left diaphragmatic nerve. 

 It passed directly from the base of the heart to the anterior face of the diaphragm, being sus- 

 tained in the middle of the corresponding portion of the pleural cavity by a special fold, 

 analogous to that of the posterior vena cava in the right pleura. 



