. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 136 COMPARATIVE ANATOMY. central nervous system in the lower Vertebrata. In higher Verte- brates, its double nature persists only in the region of the vertebral column, the two layers becoming fused in the cranial portion. As the brain of Fishes by no means fills up the cranial cavity, a large lymph-space lies between the dura and pia mater; this cor- responds to the so-called sub-dural space of the higher Vertebrata. A differentiation of the primary vascular membrane of the brain and spinal cor
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 136 COMPARATIVE ANATOMY. central nervous system in the lower Vertebrata. In higher Verte- brates, its double nature persists only in the region of the vertebral column, the two layers becoming fused in the cranial portion. As the brain of Fishes by no means fills up the cranial cavity, a large lymph-space lies between the dura and pia mater; this cor- responds to the so-called sub-dural space of the higher Vertebrata. A differentiation of the primary vascular membrane of the brain and spinal cord into pia mater and arachnoid takes place in the higher Vertebrates, and these two layers become separated in those places where there are deep depressions be- tween the individual parts of the brain; the deeper of these (pia). FIG. 109.—BBAIN-MEMBRANES OF MAN. (After Schwalbe.) DM, dura inater ; SR, sub-dural cavity; A, arachnoid ; PM, pia mater; GR, gray cortical substance of the brain. adheres closely to the brain, and also penetrates into the ventricles in the forzn of telre choroidese and plexus choroidei, while the superficial one (arachnoid) simply bridges over the depressions. No certain explanation can as yet be given of the morphological meaning of the hollow anterior end of the spinal cord in Amphi- oxus, nor of the diverticulum connected with it which opens freely to the exterior on the dorsal surface. Fishes, The Cyclostomi show a very low condition of the brain, which in many points remains in an embryonic condition. This is particularly the case in the larval condition (Ammocoetes, Fig. 110), in which the brain possesses a narrow and elongated form. The individual vesicles Jie in an almost horizontal direction one behind the other, and it is of great important^ to note that. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfec
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherlondonnewyorkmacmi
