COMMENTARY OI^ CHAPTER X. 



Since the publication of the first edition of this work, there have 

 appeared reasons for modifying the account of the brain in the 

 following respects : {a) The structure of a few parts ; (6) the mode 

 of preparing the brain ; (c) the names of certain parts ; {d) the 

 general constitution of the brain ; (e) the general system of nomen- 

 clature. 



(A) The structure of a few parts. — (1.) TM eonarium of Amphibia. — The small, 

 vascular body which lies between the caudal parts of the cerebral hemispheres (§ 1095) has 

 been described usually as the eonarium (pineal body). Wyman was in doubt respecting 

 the homology (34-, 11), and the recent observations of Osborn {1, '2, 363-270) show that 

 this body is truly a plexus (supraplex) ; that immediately caudad of it is a hitherto unde- 

 Bcribed commissure (supracommissure or commissura liahenaritm) ; and between this and 

 the postcommissure is an insignificant and commonly overlooked remnant of the stalk 

 of the eonarium, that body itself remaining ectad of the cranium. In the present work, 

 therefore, on pp. 420 and 422, the name mnarium should be replaced by svpraplex. 



■ (3.) Pseudoccde. — In the present work (§§ 1397, 1315, 1163) it is stated that the two 

 halves of the septum are in contact, and that the so-called " fifth ventricle " of the human 

 brain is wanting in the cat. This statement was based upon the examination of alcoholic 

 specimens, and it is possible that there is some variation in this respect. From a more 

 recent examination of a fresh, adult brain, and from the transection of a fcetal head, 

 the senior author has described and figured the pseudocoele (50, 459, Pig. 49.) 



(3.) Thalamus. — In extension and partial qualification of the statements on p. 490 as to 

 the appearance of the thalamus as part of the floor of the procoele, see Wilder, 5G, 460. 



(B) Modes of Preparation. — (1.) Entoccdian alinjecHon.—Tlie injection of the cat's 

 coelise with alcohol was recommended in the first edition (§ 1134). It has since proved very 

 useful with the Amphibian and human brain, as described by the senior author {56, 233- 

 334). With the frog or Necturus {Menobranchua), the quantity of alcohol required is so 

 small that the injection may be made with a small syringe or even with a dropping-tube 

 •(§ 1445). The tip of the tube may be applied — not introduced — at the lura (infundibular 

 foramen) or at an orifice made in either hemisphere or in the metacoele, according to the 

 part of the brain which is to be particularly studied. The brain (preferably supported 

 upon part of the head) should be placed in water for a few moments before the injection 

 is made ; afterward in 95 per cent, alcohol. Entocoelian alinjectiou of mammalian 

 brains is most readily accomplished through the lura, and by using either a rubber 

 bulb-syringe, and repeating the operation, or a "constant pressure apparatus" so as to 

 secure the continuous alinjeetion described in the paper above named {50, 234). The 

 alcohol should simply flow into the cceliae without exerting any more pressure than may 

 keep the parietes at their normal distance from each other. 



(3.) Arterial alinjeetion should be preceded by washing out the blood of the organ with 

 weak (25-40 per cent.) alcohol injected from the basilar or a vertebral arterj-. Then the 

 ■canula is to be secured in that artery and all the other cut arteries tied. The alcohol should 

 be strong (90-95 per cent.) and the reservoir placed at least 1 meter above the brain in order 

 to obtain the needed pressure. In warm weather the tube conveying the alcohol 

 should pass through an ice box. The same process of continuous alinjectiou may be 



