76 DR. W. G. RIDEWOOD ON THE CRANIAL [May 3, 



brancliiostegal ray, a fact already pointed out by Valenciennes 

 (Hist. ISTat. Poiss. xxi. 1848, p. 11). 



Incidentally it may be pointed out as an item of evidence in 

 favour of regarding the hyomandibular as an element of the 

 hyoid arch, a view which PoUai'd has contested *, that there is 

 invariably a definite articvilation between the front of the oper- 

 cular bone and a special process from the back of the hyoman- 

 dibular, comparable with the less definite articulation between 

 the antero- superior extremities of the brancliiostegal rays and the 

 epihyal and ceratohyal. 



It is generally assumed, and the results of the present investi- 

 gation tend to show that the assumption is justifiable, that a 

 large number of branchiostegal rays is a primitive character. 

 The greatest number of rays occurs in Elops, which has from 30 

 to 35 on each side ; Megcdops has about 24 ; and Engraulis, Coilicc, 

 and Dussumieria from 10 to 13. Alhula has 15, but the allied deep- 

 sea genus Bathythrissa only possesses 6. The commonest numbers 

 are from 6 to 9 : Ghanos and Gymnarchus have as few as 4. 



The jugular plate present in Elops and Megcdops is not defi- 

 nitely related to the hyoid arch, but, on the contrary, is united by 

 ligament with the mandibular symphj^sis. Functionally, at all 

 events, the jugular plate belongs to the branchiostegal series, and 

 it is more convenient to treat it under this heading than else- 

 where. Parker's recognition of the urohyal as a basibranchiostegii.l 

 is altogether erroneous. The urohyal is never superficial and does 

 not support the gill-cover ; it is an ossified tendon of the lingual 

 retractor muscles (see " Hyobranchial Series" below). 



Hyohranchial Series. — The unfoi'tunate application by Parker 

 (Phil. Trans, vol. 163. 1873 (1874), p. 101) of the name " basibran- 

 chiostegal" to the urohyal bone has occasioned much confusion, 

 and in spite of the unsuitability of the term it continues to be 

 employed by certain writers, and appears in a paper published as 

 recently as 1901 (Supino, Ric. Lab. Anat. Univ. Roma, viii. 3, 

 1901, p. 18). Even if the urohyal could be shown to belong to 

 the branchiostegal series, the prefix basi- would be misleading as 

 implying homology with the component parts of the copular 

 skeleton, for the branchiostegal rays are dermal, not visceral 

 bones. As a matter of fact, the urohyal is an ossified tendon, or 

 an ossification of the intermuscular septa, as Pgirker himself 

 admitted, lying between the two sternohyoid muscles t, and is 



* Anat. Anz. x. 1895. By his describing the Teleostean skull as metautostylic 

 (p. 25) I conclude he regards the hj'omandibular as a part of the mandibular arch ; 

 at all events he considers the hyomandibular of the Teleostean to be homologous 

 with the prespiracular cartilage of Sharks, which, from its position in front of the 

 spiracle, is undoubtedly a constituent of the mandibular and not of the hyoid arch. 



f Gegenbaur (Morph. Jahrb. iv., Suppl. 1878, p. 17) writes : — " Er dient, wie sonst, 

 zur Insertion der subbranchialen Muskulatur, und hat weder zur Membrana branchi- 

 ostega noch zu den Kiemenbogeu irgend eine Beziehung." See also Vetter, Jena. 

 Zeitschr. xii. 1878, pi. xiii. lig. 10, Htli. Giinther (' Study of Fishes,' 1880, p. 91) says 

 that the urohyal " separates the musculi sternohyoideij and serves for an increased 

 surface of their insertion." 



