File:Origin of Vertebrates Fig 096.png

English: Median sagittal section through a young Thelyphonus. A the front end of the body is seen the median eye (ce), o is the mouth, Ph the phanynx, œs narrow oesophagus compressed between the supraoesophageal (supr œs) and infraoesophageal (infr œs) brain mass which opens into the large alimentary canal (Al); Olf pass is the olfactory passage to the mouth, lined with thick-set, very fine hairs, which spring from the hypostome (Hyp) as well as from the large conspicious camerostome (Cam) which limits this tube anteriorly. The space between the camerostome and the median eyes is fiiled up by the massive chelicerae, which are not shown in this section, as they begin to appear in the sections on each side of the median one. The muscles of the pharynx and the muscles of the camerostome are attached to the pre-oral entosclerite (pr ent). The post-oral entosclerite is shown in section as post ent. The dorsal-vessel, or heart, is indicated as H.

Abbreviations:

• Al – alimentary canal
• bat – long, closely set sense rods
• ce – median eye
• Cam – camerostome
• H – heart
• Hyp – hypostome
• o – mouth
• œs – oesophagus
• Olf pass – olfactory passage to the mouth
• Ph – pharynx
• post ent – post-oral entosclerite
• pr ent – pre-oral entosternite
• supr œs – supraoesophageal brain mass
• supr œs – infraoesophageal brain mass