250 Mil. E. p. ALLIS ON THE OTIC REGION OF 



in tlie grooves of difierent specimens of this fish, and of the 

 irregularities in the epiotic and lateral occipital ridges. A stout 

 tendon arises from the hind end of the spheno-pterotic ridge, 

 and, running posteriorly, at first lateral to the thymus but later 

 ■enveloped in that gland, gives insertion to an anterior extension 

 of the trunk-muscles ; this tendon thus representing the stout 

 posterior process of the teleostean pterotic, w^hich is wanting in 

 Lepiclosteus. This tendon spreads posteriorly, and a part of it is 

 inserted on a ventral process of the suprascapula, and anotiier 

 part on the large occipito-supraclavicular ligament ; these attach- 

 ments suggesting the ligament which, in certain of the Teleostei, 

 jreplaces the pedicel of the suprascapula of others of those fishes. 

 The occipito-supraclavicular ligament is a large tough fascia 

 which arises fi'om a process on the lateral surface of the basi- 

 •occipital, lies upon the external surface of an anterior extension 

 of the trunk-muscles which has its insertion on the lateral surface 

 of the cranium ventral to the vagus foramen, and is inserted 

 mainly on a process along the internal surface of the lateral 

 edge of the supraclavicula, but partly also on the clavicle. 

 The levator and adductor operculi, and the levatores arcuum 

 branchialium, a.rise from the cranial wall ventral to the ligament 

 that represents the posterior process of the pterotic, and anterior 

 to the groove for the thymus. A stout aponeurotic formation, 

 which extends ventro-posteriorly into the trunk-muscles, arises 

 from the epiotic process, and that process is evidently developed 

 in relation to it. The epiotic ridge is strongly developed and 

 is certainly largely of membrane-bone, the line of the ridge not 

 even following the line of the posterior semicircular canal, as it 

 •does in many of the Teleostei. 



There is thus in Lepiclosteus, as Veit stated, no functional 

 temporal fossa, but there is a supraotic depression which, if 

 invaded by the trunk-muscles through the interval between the 

 epiotic process and the hind end of the spheno-pterotic ridge, 

 would give rise to that functional fossa, and a small anterior 

 extension of the trunk-muscles is in position so to invade it. 

 If the trunk-muscles were to invade it they would evidently tend 

 to deepen it by cutting into the massa angularis from behind 

 and above, and this would give rise to a. temporal groove similar 

 to that in Amia, wdiich would not, primarily, extend anteriorly 

 beyond the anterior semicircular canal. The development of an 

 autopterotic, a.nd the accompanying reduction of the dermo- 

 pterotic, would then give rise to the temporal groove of Scorpcena 

 (Allis, '09). this groove naturally lying mesial to the line of 

 fusion of the dermo- and auto-components of the pterotic, and 

 hence mesial to the latero-sensory canal that traverses that bone. 

 If the trunk-muscles were then to push forward dorsal to the 

 anterior semicircular canal, the groove of Scomber would arise, 

 the anterior prolongation of the groove so formed lying dorsal to 

 the parietal and frontal, being much less deep than its primitive 

 ^posterior portion, and being separated from that portion by 



