MINOR ABNORMALITIES— DEFECTIVE LOWER JAW, ETC. 51 



DEFECTS OF THE LOWER JAW. 



Grave defects of tho lower jaw are less common than pug-noses or round-heads. The two 

 best examples I have come across are provided by the gurnard (Triglot guvnardus). 



One is a jar specimen in the Glasgow Corporation Museum showing a good large head of this 

 fish severed from the body and mounted whole. The mandibular arch is extremely small, lying 

 entirely under cover of the upper jaw and hardly reaching forward to the middle of the roof of the 

 mouth. The chief prominence below the mouth is formed by the mesial portion of the hyoid arch. 

 The other is a similar specimen described in some detail by Johnstone {118). Regarding the 

 osteology of the lower jaw, this author notes that the angulars are not recognisable as separate 

 elements, while the articulars are short and placed almost vertically. Joining the distal ends of the 

 two articulars is a hoop-shaped element, which was taken as representing the united and ossified 

 Meckelian bars. 



Profound defects of the lower jaw sometimes accompany cyclopia (pp. 42, 44), but here survival 

 will be impossible. Donnadieu {58), however, gives an account of an adult carp, showing what may 

 be described as semi-cyclopia, accompanied by malformations of both upper and lower jaws. The 

 muzzle is shortened ; the eyes approach the middle line ; the skull ends abruptly above the eyes ; 

 olfactory openings are wanting ; the whole face looks downwards and to the right ; the shortened 

 upper and lower jaws are in great part united together, and the mouth is reduced to a small, 

 somewhat circular, opening 3 mm. in diameter, lying below the right eye. Lowne {146 p. 55) 

 also notes an example in the carp in which there is deficiency of the face in front of the eyes, the 

 lower jaw being defective. (See also p. 62.) 



Causation. It seems likely that defective conditions of the lower jaw may arise in the two 

 different ways already described in connection with cyclopia, pug-head, etc. — (1) as autogenetic 

 developmental aberrations (probably the two gurnard specimens and certain examples of higher 

 animals, including mammals, showing similar malformations), or (2) as the result of interference with 

 normal development through pressure or some other factor external to the embryo itself. 



HUMP-BACK AND ASSOCIATED CONDITIONS. 

 (Hog-back ; shortening of body or of tail ; twisting of body or tail.) 



This deformity has been noted time and again, even in large-sized fish, not only among the 

 Salmon u/ae, but also in many other families. 



Salmonidae {adult). Barrington 10; Couch 4-5', Day 54 II. 98, 102; Gunther 86; Hofer 

 {96a p. 307); Lowne 14,6 p. 94; Malloch 14.7a; Ritchie 207 ; Stoddart 239; Yarrell 275. 



Specimens have been sent to the author by Henry Laniond, Esq., and others, and probably 

 every angler of experience has had examples to his catch. As regards early stages, nearly every one 

 who has paid attention to fish hatcheries, notes the occurrence of embryos, the bodies of which show 

 practically every form, degree, and locality of curvature (Bugnion 34)- 



Other Fishes: 



Of other adult fishes the perch provides a number of instances, e.g. Day {54 I- 4), Lowne {146 

 p. 94), Houghton {99 p. 4), Howes {102a). Examples in Mugil chelo, M. capito, Awjuilla and Labrax 

 lupus, are put on record by Ninni {168). A very striking example in the cod is described by Storrow 

 ( .' /'/). It has long been known that in certain localities, e.g. the Firth of Forth, the cod sometimes 

 shows a particular deformation of the body due to shortening and coalescence of vertebrae (Cobbold 

 41"), Dyce {61a), Smith {228a), etc. This is the so-called Lord Fish of Yarrell, and seems to have 

 been counted by some naturalists as a separate species (see Smith loc. cit. and also Day 54 2/6-8). 

 In the sole, two instances are recorded by Howes {102a), while Lowne {146 p. 94) has also a note 

 on an example from this species. The former calls attention to Hyrtl's important paper {1021) on 

 Synostoses in the vertebral column of fishes, and notes that examples were also described by 



