The Anatomy of Chlamydoselachus 



397 



should be consulted by anyone wishing a more complete account than is given here. 

 Most of the pharyngeal muscles are represented in Text-figures 64 and 70 after Gregory 

 (1933). The interarcuales dorsales (lad.) and subspinales (S.sp.) are shown in Text-figure 

 71, after AUis (1915), drawn from a specimen in which the interarcuales are somewhat 

 atypical. In Text-figures 64 and 71 the methods of numbering the interarcuales differ, 

 so that AUis's interarcualis IV corresponds to Gregory's interdorsaHs V. 



Text-figure 71- 

 Ventral view of the roof of the pharyngeal 

 cavity of Chlamydoselachus, after the lining mem- 

 brane has been removed, showing the pharyngo- 

 branchial cartilages, efferent arteries and inter- 

 arcuales dorsales muscles in natural position. 



cc, common carotid artery; Coe, constrictor of the esophagus; 

 eal, efferent branchial artery of the first branchial arch; 

 eall, efferent branchial artery of the second branchial arch; 

 EB II, epibranchial cartilage of the second branchial arch; 

 EPB VI, epi-pharyngobranchial cartilage of sixth branchial 

 arch; HMD, hyomandibular cartilage; lad IV, musculus 

 interarcualis dorsalis between arches IV-V; ladhy, musculus 

 interarcualis dorsalis between hyoid and first visceral arches; 

 Ida, lateral dorsal aorta; !m!i, ligamentum mandibula' 

 hyoideum; n., cut ends of nerves to tissues of roof of branchial 

 chamber; PB I, pharyngobranchial cartilage of first branchial 

 arch; PB IV, pharyngobranchial cartilage of the fourth 

 branchial arch; Rabd, musculus retractor arcuum branchialium 

 dorsalis; Ssp, subspinaUs muscle; tiad, ligamentous sheet 

 formed by tendons of musculi interarcuales dorsales. 

 After Alhs, 1915, Fig. 1. 



Davidson (1918) classified the pharyngeal (branchiomeric) muscles of Heptanchus 

 as follows: (1) superficial circular [constrictor] muscles; (2) interarcuales; (3) subspinales; 

 (4) adductors; and (5) the hypobranchials. For reasons concerned with the mode of 

 development, the hypobranchials have already been considered under the category 

 of metameric muscles, though it is more common to include them with the pharyngeal 

 group, to which they functionally belong. 



All observers agree that the adductor mandibulae of Chlamydoselachus is "a thick 

 massive muscle, filling up the concavities on the outer side of the palatoquadrate and the 

 mandible" (Goodey, 1910.1, p. 547)- In all the illustrations (by various authors) of this 



