182 THE NERVOUS SYSTEM. 



in a sheath of endothelium continuous with that of the general 

 cavity. 



The three anterior cutaneous nerves pierce the Fascia dorsalis near 

 the spinous processes, the fourth a little to the side, the fifth perfo- 

 rates the 31. coccygeo-iUacus at about the junction of its anterior and 

 middle thirds; the sixth and seventh perforate the same muscle, 

 but more posteriorly. There are seven of these Rami cutauei, the 

 first coming" from the second spinal nerve, the rest from the suc- 

 ceeding six spinal nerves. 



B. The Ventral Branches. 



The ventral branches of the spinal nerves are larger than their 

 corresponding dorsal branches : each nerve gives off inunediately 

 a Ramus communicans to the sympathetic system (Figs. 117 SM, 

 120 C); these Rami communicantes will be described with the sym- 

 pathetic system ; the remaining portions of the ventral divisions of 

 the original spinal nerves are usually known as the spinal nerves ; 

 they will be described as such in detail. 



1. The hypoglossal nerve ^ (iV. hijpoglossus, N. sjnnalis I), (Figs. 

 114, 115, and 117 Ml), or first spinal nerve, is of small size; it 

 leaves the vertebral canal between the first and second vertebrae to 

 lie between the Musctili intertransversarii and the pharynx, where it 

 has in front the Arferia vertehralis, behind the Arteria and Nervus 

 hrachialis ; passing under the Levator anguli scajiulae, it touches the 

 Aorta ascendens and crosses the Vagus and the Carotid-gland, and 

 thus reaches the space between the Muscnli sterno-hjoidei and the 

 Retro-hyoideus ; then curving forwards sharply it turns under the 

 Mylo-liyoideus to course between the fibres of the Genio-hyoideus to 

 the root of the tongue, where it ends. It first lies to the inner and 

 then to the outer side of the glossopharyngeal nerve. In its course 

 the nerve gives off the following branches : — 



{a) One or two communicating twigs (Figs. 1 14 and 122) to the 

 second spinal nerve. 



* [Observers have differed considerably as to the relations of this nerve : Volkmann 

 describes it as the first nerve of the neck, and describes a ganglion on its dorsal 

 root ; Vogt denies the presence of this ganglion, and regards it as a true cranial 

 nerve ; Stannius asserts that no ganglion exists, and holds the nerve to represent the 

 first two spinal nerves ; Wyman describes the two roots and regards it as a spinal 

 nerve ; Hoff'mann regards this nerve as the second spinal (N. spinalis II) : Fiir- 

 bringer as the representative of two spinal nerves ; de Watteville describes two roots 

 and names it first spinal nerve. — Tkans.] 



