1174 



SCAXDIXAVIAN I-ISHES. 



ill batrachian lar\;v (tig. 344), a reminder that in tiieir 

 origins these two types were structurally not far re- 

 moved from each other. Tiic tongue of the Lampreys 

 contains a long rod-like su]iportiiig apparatus, capable 

 of protrusion and retraction, and suspended under the 

 ceratohyal. This ai)paratus consists of two cartilages, 

 an anterior, semipateriforui, excised in front, situated 

 in the mouth, and a posterior (jtlnj), much longer, the 

 posterior extremity of which projects into the branchial 

 l)asket. It is interpreted as homologous with a basihyal, 

 and the anterior cartilage liears the lingual teeth (fig. 

 34.5), at the very tip a curved, transversal dental plate 

 {((h/). with firm, rounded and obtuse teeth, and further 

 l)ack two plates (plii). lying more loosely in the gums, 

 meeting anteriorly in an ellipse, and furuislied with 

 small but acute, retral teeth. 



The whole oral apparatus of tiie Lampreys, which 

 is aljundantly su])plied with cartilages, paired and un- 

 paired, ]jateriform or lamellar and rod-like — one of 



I, 1 I iihi f I 



Fig. 344. Cartilaginous parts etc. in tlie head of a tadpole about 

 1 in. long, at the time when the hind legs begin to appear. 

 About 9 times nat. size. After P.4RKER. 

 (■()', n. and et, as in preceding figure; Mh, Thl, and Me, the three .in- 

 terior divisions of the brain; Oc, eye; als (alisphenoid), pro, (prootic), 

 pto (pterotic), so (supraoecipital), en (exoceipital), and op (opisthotic), 

 all answering to t in preceding figure ; dr., section of the skin ; G, gill- 

 opening; br, as in preceding figure; Inn and sj)l. answering to spl m 

 preceding figure; fo, as in preceding figure; liy, answering to j^l'y '" 

 preceding figure; Ip, lips (dermal flaps); mck, Meckelian cartilage; 

 7ndl', mandible; i]u, quadrate bone; ma.r, upper jaw. 



them annular — belongs to the extravertebral structures. 

 Below the cormta trabectdanim (fig. 343, ctr) is medially 

 situated an invertedly pateriform cartilage (the median 

 cartilage of the roof of the mouth, ))ie(). MCller's "vor- 

 dere Deckplatte des Mundes"), which has behind it on 

 each side a flatlj- convex cartilage of a rounded quad- 

 rangular form (the posterior laterttl cartilage of the 

 roof of the mouth, Ip, Mi ller's "hintere Seitenleiste") 

 and at about the middle of its side-margin a narrower, 

 more terete plate (the anterior lateral cartilage of the 



roof of the mouth, la. Miller's "vordere JSeiteideiste"). 

 Ll^nder and before the said median plate lies the annular 

 cartilage (ann, Muller's "knorpeliger Lippenring"), the 

 bearer of the largest teeth, which has behind it a me- 

 dian plate (the sublingual ctirtilage, si, MCller's so- 

 called "Zungenbein"), situated under the tip of the hyoid 

 bone, in front expanded and convex, behind acutely 

 elongated. On each side of this sublingual plate lies 

 behind the annular cartilage a rod-like cartilage (the 

 lateral labial cartilage, laf, Muller's "sfielformit/er 

 Anhang des Lippenrhuies"); and three small cartilages, 

 the bearers of the lateral teeth of the mouth, lie loosely 

 in the skin on each side of the annular cartilage. 



The branchial basket {hr) too is entirelj- extra- 

 vertebral, a network of thin flat cartilaginous rods, su])- 

 porting the outer walls of the gill-sacs. Anteriorly this 

 network is suspended from the epihyal cartilage; pos- 

 teriorly the cartilaginous mass developes into a saccate 

 case for the heart, a pericardial cartilage {pre). 



Tlie nervous S3stem of the Lampreys has thrown 

 light, especially in two points, on the morphologj' of 



Fig. 345. Tip of the tongue and its dental plates in a Lauipern 



{Petromyzon fliiviatilis), X about 5. 



aln, anterior dental plate of the tongue; pin, posterior dental plate 



of tlie tongue. 



the higher vertebrates. These points have reference to 

 the interpretation of two organs still involved in great 

 obscurity, the cerebral appendage and the pineal gland. 

 At the bottom of the human cranial cavity, as well 

 as on the under surface of the lirain in all other true 

 vertebrates, lies a glandiform organ whose function is 

 still doubtful. It is known anatomically as the hijpo- 

 physis cerebri. In man it is about as large as a pea, 

 oblong in form and transversally set, lodged in the de- 

 pression on tlie ui)per surface of the sphenoid bone 

 (the so-called sella turcica) and attached to the brain by 

 a funnel-shaped prolongation thereof in a downward 

 direction from the bottom of the third cereliral ventricle. 

 It consists of two parts, an anterior, the development 

 of which we shall now describe, and a posterior, whose 

 development originates from the brain. Great impor- 

 tance was formerly attributed to it both by physiologists 

 and psychologists. B}- Galen, in the second century 



