. A manual of zoology. Zoology. IV. VERTEBRATA 473 innervate the somatic musculature, the dorsal roots supply both the sensory apparatus and the visceral muscles. One of the most striking facts in the question of the segmental nature of the cranial nerves is the relation of these to the visceral arches, the trigeminal in front of the mandibular, the facial in front of the hyoid arch, and the glossopharyngeal and vagus with similar relations to the gill arches. Besides the nervous system of the body already outlined, the verteVjrates have a special ner\'0us system supplying the viscera, the sym
. A manual of zoology. Zoology. IV. VERTEBRATA 473 innervate the somatic musculature, the dorsal roots supply both the sensory apparatus and the visceral muscles. One of the most striking facts in the question of the segmental nature of the cranial nerves is the relation of these to the visceral arches, the trigeminal in front of the mandibular, the facial in front of the hyoid arch, and the glossopharyngeal and vagus with similar relations to the gill arches. Besides the nervous system of the body already outlined, the verteVjrates have a special ner\'0us system supplying the viscera, the sympalhctic system, and in this a special central organ consisting of right and left cords beneath the vertebral column, in which ganglia are incorporated. The last of these ganglia lies at the base of the caudal vertebrae, the most anterior at the beginning of the neck. From the latter nerve cords extend into the head and are connected with ganglia {otic, sphenopalatine). This system sends out nerves in the form of delicate networks (plexus sympalhclici) which usually accompany the blood-vessels to the vegetative organs (intestine, sexual apparatus, etc.). It is also connected with the spinal nerves. The space between the central nervous s)^stem and the surrounding skeleton is large in fishes and is tilled with a loose fatty tissue which, close to the nervous mass, is thickened to a richly vascular envelope {mcninx) of the brain and spinal cord. In the groups from amphibia to birds this primitive meninx is divided by the development of a subdural lympli space into two layers, the dura mater and the pia mater. The pia, which in mammals differentiates a delicate arachnoid membranehy the for'msition of numerous lymph spaces, is next to the nervous system and is the vascular layer, while the dura is a tougher membrane wdiich approaches and fuses with the periosteum lining the skull in proportion to the extent that the brain fills the cranial cavity. In the ver- tebral column the dura
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
