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F. The Nervous and Muscular Systems and Sense Organs {second frog). 



1. Eeflect the skin along the back and notice the large lymph spaces, the cutane- 

 ous branches of the dorsal nerves crossing them, and the position of the 

 lymph hearts — one at each side of the urostyle, and one within the margin of 

 each supra-scapula. 



2. Examine the following muscles — 



(a) The depressor mandibuli, which extends from the skull over the scapula 



to the angle of the jaw. 

 (6) The trapezius, extending from the exoccipital to the dorsal border of 



the scapula. 



(c) The lattissimus dorsi, extending from the dorsal fascia behind the scapula 



to be inserted into the deltoid ridge of the humerus. 



(d) The temporal, passing from the auditory capsule to the coronoid pro- 



cess of the mandible. 



(e) The pterygoid, which rises in front of the temporal and is inserted 



into the mandible behind the coronoid process. 

 (/) The masseter, from the quadrato-jugal to the outer surface of the 



mandible near its articulation. 

 Observe that (d), (e), and (/) elevate the mandible. 

 The pectoral girdle and sternum should now be examined (see page 8). 



3. After noting, clear away the infraspinatus, levator anguli scapulae, and retrahens 



scapulse, and also the extensor dorsi communis and intertransversalis muscles, 

 and the right snpra-scapula. Cut across the membrane between the skull and 

 the atlas, and then remove carefully the roof of the cranium so as to expose the 

 brain by cutting from the foramen magnum first through the side walls, and 

 then across in front of the parieto-frontals. Expose the spinal cord and 

 filum terminale by removing the neural arches and the upper segment of the 

 canal of the urostyle. 



4. Eemove the pigmented pia mater, note and draw (3 nat. size) the olfactory 



and cerebral lobes, the optic thalami (indicating the position of the pineal 

 gland, probably removed with the roof of the sl5,ull), the optic lobes, cerebellum 

 and medulla oblongata, and the spinal cord (showing the brachial and lumbar 

 enlargements), the dorsal fissure, and the filum terminale. 



5. Examine the cavities of the brain. 



(a) The fourth ventricle, a triangular space behind the cerebellum roofed 



over by a vascular membrane. 

 (6) The iter, a narrow passage leading from the fourth to the third 



ventricle. 



(c) The cavities of the optic lobes which communicate with the iter. 



(d) The third ventricle situated between the optic thalami and covered by 



the choroid plexus. Eemove the plexus, noting the hollow peduncle 

 of the pineal gland projecting from the roof of the ventricle, the band 

 of fibres known as the posterior commissure, also the infundibulum 

 projecting downwards towards the pituitary body. 



(e) The lateral ventricles. Each communicates by a small aperture (the 



foramen of Monro) with the third ventricle, and extends a short 

 distance into the olfactory lobe. 

 In an outline sketch of the brain (3 nat. size), indicate the cavities 

 mentioned. 



6. Examine the olfactory bulbs, and expose the olfactory sacs in order to see the 



smelling membrane in which the olfactory nerves terminate. 

 Make a sketch (4 nat. size) showing the two chambers (one opened) and 

 the olfactory nerves. 



